In excess of 475,000 heavy duty pickups were sold in the United States last year – the capable workhorses represented more than 25 percent of the year's full-size pickup volume. But unlike the passenger-car segment, where dozens of makes and models are constantly competing for supremacy, the heavy-duty segment consistently boils down to a four-way battle between the Ford F-250 Super Duty, Ram 2500 and the Chevrolet Silverado 2500HD/GMC Sierra 2500HD twins. And, while today's automobile shoppers seek fuel economy, safety features, style and technical innovation, big truck buyers are essentially on a quest for one attribute: capability.

General Motors recently invited us to Arizona to explore the power, proficiency and potential of its new 2015 Sierra and Silverado HD trucks. After a day of driving and hauling, we walked away with a much better understanding of what makes these 7,500-pound hulks of diesel-consuming machinery appealing.
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This past September's State Fair of Texas was chosen as the launch venue for GM's model year 2015 heavy-duty trucks. While the vehicles aren't all-new (the chassis was redesigned for the 2011 model year), each debuts with fresh new cabs, upgraded interiors and a host of improvements on the heels of the recent half-ton Silverado/Sierra redesign.

More than two-thirds of all buyers opt for the mighty Duramax 6.6-liter diesel.

Allowing consumers to build a truck to suit their needs, GM will continue to offer more than 150 combinations of HD pickup that includes the buyer's choice of bodystyle (regular, double or crew cab), drivetrain (two- or four-wheel drive), bed length (6.5-foot or 8-foot), axle ratio and one of three powerplants. As the automaker rightly points out, "One size does not fit all."

The HD range's base powerplant is a gasoline-burning 6.0-liter Vortec V8, rated at 360 horsepower and 380 pound-feet of torque and running through a six-speed automatic transmission. The second engine choice is a modified bi-fuel version of the same 6.0-liter V8, which runs on gasoline or compressed natural gas (CNG). The last engine, which more than two-thirds of all buyers opt for, is the mighty Duramax 6.6-liter diesel (pictured below). The turbocharged engine is rated at 397 horsepower and 765 pound-feet of torque and it sends its power through an Allison 1000 six-speed automatic transmission.

While the EPA doesn't post fuel economy figures for this class of vehicles, owners reporting online to Fuelly averaged about 15 mpg overall in 2013 models (our diesel test vehicle displayed about 18 mpg on the open highway when driving without a load, but our mileage dropped significantly when the truck was tasked with hauling or towing).

2015 Chevrolet Silverado 2500 HD

Both Silverado (and Sierra) HD pickups are covered by a three-year/36,000-mile limited warranty, five-year/100,000-mile limited powertrain warranty, and the automaker will provide two-years/24,000-miles of scheduled maintenance, including refills of diesel exhaust fluid (DEF), at no additional charge (oil change intervals are determined by service use, but GM estimates that the five-gallon DEF tank needs to be refilled about every 5,000 miles).

The HD trucks are rated to tow 19,600 pounds.

Underpinning the family of trucks are fully boxed steel frames. The front suspension is independent, with forged steel upper control arms and cast iron lower control arms. Torsion bars are used instead of springs to allow easy trim height adjustment, says GM. The rear suspension utilizes three-inch wide asymmetrical leaf springs. There are disc brakes at all four corners, with two-piston sliding calipers on the front and a single-piston sliding calipers on each rear. With a conventional hitch, the HD trucks are rated to tow 19,600 pounds. A fifth-wheel setup increases the towing rating to 23,200 pounds.

The cargo beds are new, and they have both been redesigned to incorporate better illumination, additional tie-downs, EZ Lift and Lower tailgates and convenient CornerStep bumpers (which were touted on the 1500-Series trucks last year but actually introduced on the now-discontinued Avalanche). A factory spray-in bedliner is optional. GM is touting its best-in-class bed payload capability, an impressive 7,374 pounds.

In other mechanical news, GM has fully integrated the cruise control with the engine and transmission, thus allowing the driver to maintain consistent speeds up and down grades without having to manually downshift gears or apply the brakes. In addition to reducing workload, the system, which uses the functions of Auto Grade Braking and Diesel Exhaust Braking (on Duramax models), is claimed to prolong brake life and help prevent the friction brakes from overheating. GM's StabiliTrak with Trailer Sway Control is standard on all models, including the big 3500-Series dually.

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Aerodynamics have played a big role in determining their shapes.

In terms of exterior appearance, like their half-ton relatives, GM's new HD trucks remain conservatively styled. They're best described as offering traditional pickup designs, with uniquely shaped hoods, grilles and headlamps used to differentiate between Chevy and GMC models. Aerodynamics have played a big role in determining their shapes, and GM engineers went to great pains to explain how they sculpted the bodywork to provide more airflow to the engines while reducing wind noise in the cabins. While some competitors in the segment, like Ram, have been successful with brawny and burly styling to emphasize ruggedness, these GM offerings are less dramatic and unlikely to offend. Overall, we like the looks of the GMC Sierra Denali the best, as its massive chrome grill provides the most aggressive character of the bunch. Our Chevy Silverado 2500 LTZ test vehicle, with its busy front end plated in slats of chrome, is arguably the least attractive in the family.

The interior is GM's headline story for 2015. Gone is the ho-hum cabin of last year's model, now completely replaced with an interior that essentially mirrors that of GM's half-ton lineup. Large, vertical vents at four positions provide plenty of cabin airflow, while the center cluster is reserved for infotainment, climate and auxiliary controls. At the bottom of the latter is a large storage compartment configured with a 110-volt outlet, five(!) USB ports, four 12-volt outlets and an SD card slot. Standard models are offered with an analog six-gauge instrument cluster (as seen below), but higher grade models incorporate a multi-function color display at the bottom. The real eye candy is found within the range-topping GMC Denali models, which are configured with an analog tachometer and speedometer and a large multi-configurable digital display between the two. As expected, all of the models are offered with The General's latest eight-inch infotainment display with IntelliLink connectivity suite.

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GM brought a dozen or so trucks to its Phoenix-area event, including a couple of Ford and Ram models for comparison. Given that the Chevrolet and GMC are mechanically identical, we chose to focus our attention on the automaker's volume model, the Silverado 2500 HD diesel.

The new cabin is spacious, comfortable and very functional.

Our test vehicle, a 2015 Chevrolet 2500 4WD LTZ Crew Cab, arrived painted Deep Ruby Metallic and carrying a base price of $48,230. A total of $12,140 worth of options, including the Duramax 6.6-liter V8 ($7,195), Allison six-speed transmission ($1,200), power sunroof ($995), 20-inch forged wheels ($850), MyLink audio ($495), spray-in bedliner ($475), dual alternators ($295), camper mirrors ($55) and destination ($1,095) pushed its as-tested MSRP to $61,465.

Considering that we've had good things to say about the half-ton cabin, it's no surprise that we like the three-quarter ton's accommodations as well. The new cabin is spacious, comfortable and very functional. A tilt/telescoping wheel, power seats and available power-adjustable pedals mean drivers of all statures will fit well behind the leather-wrapped, multi-function, four-spoke steering wheel. The second row is equally as accommodating, but a short stint back there did reveal that the optional front ventilated seats exhausted warm air onto our knees, oddly heating the two occupants seated behind the driver and front passenger.

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The driving position in a HD truck is properly commanding, elevated well above other traffic, but sitting up so high does pose its own set of difficulties. Outward visibility from the driver's seat of the Silverado HD remains challenging, especially looking downward at other low vehicles and during parking maneuvers, because its slightly lower seating position blocks the view of the ground immediately next to the chassis. After comparing the Chevy back-to-back with its competitors, it's clear that rival Ford offers the best outward visibility (that automaker wisely scoops out the top leading edge of its doors to improve downward sightlines), with the tall seating position of the Ram coming in a close second.

Outward visibility from the driver's seat of the Silverado HD remains challenging.

We spent the morning putting about 100 easy miles on our 2500 4WD LTZ Crew Cab with an empty bed and no trailer. But in the afternoon, we grabbed the keys to a few other trucks that were loaded with heavy payloads (3,750 pounds of weight in the bed) and towing heavy trailers (10,000 pounds, combined trailer and load). We were allowed free rein to run the trucks around town, though the canyons, or up a nice, long highway grade. And, as previously mentioned, GM brought a Ford and Ram along for comparison.

In general, GM's new HD trucks drive very well. Their steering effort (the HDs retain hydraulic steering with belt-driven pumps) and accelerator springs are both on the heavy side when compared to the competition, but the additional muscle required to move the controls helps to make them feel more substantial on the road and decidedly more stable (remember how nice BMW's heavy steering used to feel?). Transitional handling is understandably a challenge in vehicles weighing more than three tons, but the big trucks are much more agile than most would expect and they never feel unstable.

2015 Chevrolet Silverado 2500 HD

Accelerating the GM HDs off the line involves a bit of lag, as their single variable-geometry turbocharger spools up, but a rush of power effortlessly launches them down the road. Their big diesel engines redline at 3,200 rpm under acceleration (yet they will overrun to 4,800 rpm during braking) and their Allison gearbox shifts smoothly as the speedometers climb. We estimate a 0-60 mph sprint in either takes about 10 seconds, which only sounds slow on paper. In real-world driving conditions, such as running around town, climbing the onramp or passing on the highway, their acceleration isn't a reason for concern (GM electronically limits the top speed of its HD trucks to 98 mph due to tire construction). With all that mass, braking doesn't come close to passenger-car levels, either, but ABS and stability control ensure stops are straight and controlled.

We estimate a 0-60 mph sprint in either takes about 10 seconds, which only sounds slow on paper.

If you've been following heavy-duty trucks, you're undoubtedly well aware of the horsepower/torque battle that has been going on for years. When speaking of the competitors, Ford offers its own 6.7-liter V8 turbodiesel, rated at 400 horsepower and 800 pound-feet of torque, while Ram fits a 6.7-liter inline-six turbodiesel, sourced from Cummins, that cranks out 385 horsepower and 850 pound-feet of torque. The Chevrolet's engine, the product of a GM-Isuzu venture dating back to 2001, is right up there in the horsepower rating, but it falls well behind the other two with regards to torque.

Attempting to demonstrate that numbers don't tell the full story, GM hooked 10,000-pound trailers to a Silverado 2500, Ford F-250 Super Duty and a Ram 2500 for side-by-side acceleration tests. We lined up each combo and climbed a six-percent grade at 45 mph before mashing their throttles to the floor. In all of these highly unscientific races, the Chevrolet was the quickest to accelerate away from the others (take these results with a grain of salt, as the rear-axle ratios and wheel sizes were not identical). Our seat-of-the pants observation said the GM's Allison gearbox, which was quick to adapt to the load, was its advantage.

2015 Chevrolet Silverado 2500 HD

It's the most competent on the highway where miles pass effortlessly beneath its impressively hushed cabin.

More interesting, and easier to verify, was GM's cruise control test down a long grade with the 10,000-pound trailers in tow. With the cruise control set at 55 mph (in towing mode and with exhaust brakes activated), we watched each system attempt to hold their trucks at a constant speed. The Ford and Ram quickly rushed past 60 mph, causing us to step on the brakes, but the Chevrolet held its speed right near 55 mph during the entire test. The automaker is proud of how well it has integrated cruise control into its engine and transmission software, and the combo seems to work effectively.

We will be the first to concede that all of the players in the heavy-duty truck segment are closely matched. Yet hours spent in the Chevrolet and its two rivals reveal strengths and weaknesses in each. The Ford is the oldest of the three, which immediately shows in its dated cabin, but its powertrain and chassis remain very competitive. The Ram is hard to fault, especially if you like its styling, and its self-leveling rear air suspension is brilliant (unfortunately, our GM-supplied test truck had the standard springs and shocks). GM's offering doesn't break new ground mechanically, but it's the most competent on the highway where miles pass effortlessly beneath its impressively hushed cabin. Plus, the Chevrolet takes honors for its fully integrated suite of electronics that work seamlessly with its powertrain.

The arrival of these 2015 Silverado and Sierra models doesn't mean that any of GM's rivals are going down in flames. Instead, these new trucks are strong competitors that solidify the segment as a whole. Heavy-duty truck buyers finally have three competent choices without an obvious wrong answer.

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