Is a GMC truck just a dressed up Chevy truck?

I was always under the impression that a GMC truck was just a dressed-up Chevy truck. So my question is that if that is true, what is the allure? They cost quite a bit more to start with. I am not trying to be snarky; I am really curious.
I don't know, Pop ordered His new '76 with an 8ft. Stepside box, to be replaced with the just-discontinued stake-bed, no radio, no A/C, 350-4bbl, 4spd., 3/4ton 4×4. Hardly some luxo-level tonka-toy, lol..