The layout might look familiar.
This Sierra still has camouflage in the cabin, but it's not enough to conceal the major similarities with the new Silverado. As the image above show, they have the same center stack layout with a screen on top, vents flanking it, and HVAC controls below them. The GMC appears to have a slightly different steering wheel with vertical spokes at the bottom rather than the more curvy elements at the same location on the Chevy.
The GMC's differences will be more evident from the outside. Rather than the Chevy's skinny, horizontally positioned headlights, the Sierra's illumination has a vertical orientation. Spy shots suggest that the GMC has a large grille with a relatively simple array of horizontal slats, at least in comparison to the Silverado's two-tiered layout. Higher trims would likely have lots of chrome to make the truck stand out.
At the back, the Sierra has large, bracket-shaped taillights, rather than the Silverado's illumination that breaks up the design into separate sections.
Since the Silverado and Sierra share platforms, the GMC will surely shed some weight from the greater use of aluminum, though still with steel in the bed. Depending on a truck's precise configuration, it'll weigh as much as 450 pounds less than the existing model.
The Sierra will be available with the 5.3- and 6.2-liter V8s from the Silverado, and the 10-speed automatic will be available on some trims. It's possible that the new 3.0-liter turbodiesel could be part of the GMC's range, too.