The USA is the biggest purchasers of trucks and SUVs....in the entire world. Although Ford takes the crown for actual yearly truck sales- GMC Denali and Yukon SUVs outsell Ford/Lincoln SUVs, by a huge margin. One of the reason for this is the State Department exclusively uses black GMC SUVs for everything from shuttling our(current) stupid President around, to Homeland Security/Big-Brother uses.
Well, since GMC only makes trucks and SUVs, while Chevy has a full line of vehicles, Chevy is more widespread. But they are still both made by GM, so there really isn't a difference between GMCs and Chevy's trucks and SUVs
Same company makes both but the GMC is considered and priced as more of a high end version of the Chevrolet pickup and SUV line thus there are far more Chevrolet models on the road than GMC models.