Unlike the Toyota Prius, which is a "full hybrid" and uses an electric motor to completely power the car at low speeds and help the gasoline engine out when necessary, the Sierra 1500 hybrid just shuts down when braking to a stop, and then stays off during idle. Hybrid-wise, that's about it. The electric motor restarts the gasoline engine once the go pedal is depressed, but the battery isn't strong enough to move the big truck on its own, at any speeds, and nor does it contribute to the 5.3 liter V8's shuttling duties. The benefit of this system seems to be in name only, as the mileage for the pickup increases by a whopping 2 mpg around town and by zero on the highway. Wow, this newfangled hybrid technology is really being put to good use.