It is not as simple as that. My 2011 GM 2500HD truck has a higher payload rating than any of the SRW 3500 trucks. Only by going to DRW would I get a higher payload rating.
With my truck the only difference between the 2500 and 3500 versions was the extra set of leaf springs on the 3500 and that the 2500 was available with the extended cab which was not the case with the 3500 and the 3500 could be bought with DRW. This is true for current trucks from GM/Chevy and from Ram but not with the Ford trucks where the F-350 is in a different class that includes the F-450 and F-550 trucks.
And with Ford their F-350 pickup has a higher load capacity than their F-450 pickup truck. One needs to buy the F-450 Chassis Cab version to get a greater payload.
On dealers' lots I found in my area that most of the 3500 trucks had regular cabs and 2WD and DRW. With the GM 3500 my options were a crew cab or a regular cab, neither of which I wanted.