camp-n-family, Take a look at the axle(AXLE) name and spec's on the later models Dodge Ram HD diesels. The reason the 2500 has a lower load rating,is the lighter spring pack.... Not the axle. On a Diesel Ram 3500... The only difference in the rear differential between the SRW and the DRW, is the distance between the spring plate and the brake/hub assembly (greater distance on the DRW). The load/tow capacity of the axle (not tires,rims,springs) assembly is the same on both the 2500 and the 3500 Ram Diesel HD's.
So.... With a tire,rim,wheel,and spring upgrade you could equal or exceed the load ratings of a factory stock 3500 dually. Though you will "Not" have the wide footprint, which may/probably give more lateral stability.
I hope that this helped clean-up any questions or concerns.
All the best and Happy Trails