If there really is a difference when the GVWR goes over 4,500kg (9,900 pounds) that explains why GM used to rate their SRW 3500 at 9,900 GVWR.
You can buy a new truck with different GVWR to help with some of these legal issues.
Where I work we purchased a 2015 Chevy 3500 SRW. It's GVWR is normally 11,500 but you can order it with a sticker that says 10,000. Ours is this way because if it were over 10,000 we would have to follow a bunch of DOT regulations. It's the same truck, no difference what so ever in it's mechanical construction, just a sticker.
This is one reason I don't put a lot of stock in the GVWR of a vehicle when loading it. I generally look at the actual tire and axle weights.
