In the past, GMC trucks have been little more than rebadged Chevrolets. That's been changing in recent years, and the divide seems to be growing larger. The grille looks much larger than the Silverado's and there appears to be a small inlet right where the hood meets the front. From the side, we can see that the two trucks have different fenders and beds. The wheel wells on the GMC are squared off at the rear. Compare that to the round wells on the Chevy.
Out back, the design is far more similar. Both trucks appear to have rear-facing exhaust outlets. The taillights, too, look to have close to the same shape. A big bulge in the center of the tailgate likely hides a large GMC badge.
We still don't have a firm reveal date, but look for some further news this auto show season.