Actually, GMC was originally the heavy truck division of General Motors and Chevrolet was the the light truck division. Over the years, the company co-mingled the light and heavy trucks so that dealers who sold Buick, Pontiac, Oldsmobile or Cadillac could have a truck line without infringing on the Chevrolet dealers' protected sales territory for Chevy trucks.
If you wan't a "luxury" model chevrolet truck you need to buy a Cadillac SUV... GMC and Chevrolet trucks are identical and neither is available with luxury options that the other isn't, as far as I'm aware.