Cost
When it comes to MSRP, the Chevrolet Silverado 1500 doesn't cost much less than the Sierra 1500.
Utility
The GMC Sierra 1500 is a better choice than the Chevrolet Silverado 1500 with respect to hauling capacity, especially if you often need to carry a lot of loot or big animals.
Neither the Chevrolet Silverado 1500 nor the GMC has a marked advantage regarding seating capacity.
Towing is significantly more the GMC's forte than it is the Chevrolet Silverado 1500's.
Dimensions
Your wallet will hurt more every time you fill up the GMC than the Chevrolet because of its bigger tank.
The GMC Sierra 1500 and the Chevrolet compete for the same parking spaces.
Performance
With that kind of horsepower, both the Chevrolet Silverado 1500 and the GMC are genuine speedsters.
Warranty
The GMC Sierra 1500 and the Chevrolet have the same basic warranty.