I've heard said that the GMC frames are thicker and longer. I've never measured a pair to confirm or deny that claim. I'm not inclined to believe it mostly because I know the 1-ton frames are made of the same thickness material based on measuring both myself.
However, I'm making an assumption and that can always be dangerous.
The front cross member is different UNLESS you are looking at one of the Canadian GMC trucks that came with a Chevy motor in it. That fits into the topic what is different between US made and Canadian made GMC trucks and I prefer to defer to some of the Canadian members for those specifics.
