Originally Posted by 3'senough
Here are the actual axle and spring load capacities for each class of vehicle for GMC rear axle load 2013's.
2500, 3500 SRW, 3500 DRW
6200 / 7050 / 9375#
GMC rates them the same regardless of 2WD or 4WD.
Cargo capacities will adjust depending on model and options.
You are correct on the ratings. However my point is the actual components, axle housing all the inner components, brakes, frame, structural cross members are the same.
The suspension is the limiting difference between a 2500 and a 3500 SRW. (Leaf spring being the actual component difference)
The tires are what limits the capacity between a SRW and a DRW. If you look at the tires on a dually they are rated 3195 each. However the rear axle rating isn't 12,780, it's as you noted 9375, which tells me the axle, suspension or overall structure is the limiting factor.