Wheel/tire size isn't indicative of axle/bearing sizes.
All 2500/3500 srw Dodge/Rams have the same 11.5" AAM rear axle which AAM rates in the 10700 lb range. The 2500 is limited by its 6000-6500 rawr which is the lessor of the wheels/tires/rear spring pack ratings. Same for the front axle that comes in various weight ratings.
Before the 2500 rear coils showed up the only difference in the 3500 srw was the rear spring pack.
The Cummins option gave the truck higher front spring pack ratings and heavier front axles vs the gas version on some 2wd cab configurations.
Brakes ??
According to Dodge/Ram techs on TDR or DTR or Cummins/other forums they can carry the same brakes; such as a crew cab Cummins option 4wd.
See IB516 posts for his experience with the 2500 coils and a 12k-13k 5th wheel trailer