I believe they are actually made on the same production line, but the
same people, with just a few parts (grill, some interior parts, etc.)
being different, but I can't find any proof of that at the moment. The
engines and components are identical so any difference you are seeing is
a sample difference, not a Chevy vs. GMC difference.

Matt

I think they muse be on the same line. I have bought 3 GMS's, 2 sierras
and one 5500 in the past 4 years, still have i P/U and the 5500.
the P/U got delivered to me with a left door logo from chevy and the
rest was GME. The 5500 truck came with Chevy branded keys but is a GMC.
My bet is they came from the same line just lazy assemblers!