A GM spokesman told Motor1, "[We] did not attribute [the delay] to a single entity, as the truth is this is a collaborative effort between GM and several government entities. We will make the 2020MY Duramax available for dealers orders soon, and expect to deliver the first trucks to customers soon after emissions testing is complete."
We know the new 3.0-liter Duramax diesel has 277 horsepower and 460 pound-feet of torque, outdoing Ford's 3.0-liter PowerStroke diesel by 27 hp and 20 lb-ft. But without final EPA paperwork, GM can't release the numbers that will show how the two engines stack up when considering fuel economy and tow ratings.
The certification process has been sticky for a few other makers of late, especially since the Volkswagen Group situation in 2015. BMW had to delay the launch of four diesel models in 2016 over EPA testing. The new Ram 1500 dribbled out in a trickle last year for reasons thought to deal with EPA testing, coming as it did a year after the EPA investigated Ram's EcoDiesel engines in 2017 and 2018. More recently, WLTP testing in Europe caught out just about every automaker over there.
Since we're almost halfway through 2019, the delay until the 2020 model year is only a few months. Still, GM told dealers to cancel any orders for the engine for this model year. Dealers will need to resubmit the orders once opening begins, but GM hasn't said when production will begin other than "soon." The company said that it will offer 2020-model-year replacement vehicles to customers and dealers. If prices hold into the next model year, the 2020 Silverado 1500 and Sierra 1500 with the inline-six diesel will come at a $3,890 premium over the 2.7-liter turbo four-cylinder, and a $2,495 premium over the 5.3-liter V8.