Spy shots seem to have revealed that the GMC Sierra 1500 will offer a diesel powertrain option. There are shots of the vehicle from the underside which you can see in the article linked below. It seems to be another step in GM's plans to release more diesel powered vehicles in the future. The first officially announced being the Chevrolet Equinox who will sport 577 miles on a full tank.
1. Spy shots of the GMC Sierra 1500 have been released.
2. The spy shots seem to indicate that the vehicle has a diesel powertrain or at least it seems to hint at them.
3. A shot of the underside of the vehicle, in the article below, seems to back up that thought process.
Quote: "These photos show underneath the truck, which reveals the tank for the exhaust after-treatment fluid and the diesel particulate filter. Unfortunately, the exact powerplant remains a mystery." (Bruce, 2017)
Link to article: https://www.motor1.com/news/179316/gmc-sierra-1500-diesel-spied/