This use to be easy to answer, the last few years it has become more complicated. There was no Ram 3500 until 2003 MY. There was a 2500 'camper pkg" that got a higher GVW and rear overloads. In 2003 that went away and it was replaced with the 3500 SRW. For the most part the axles/brakes where the same between the SRW and DRW. The only difference between the 2500 and the 3500 SRW where the rear overload springs. Then in 2012MY you could get a "max Tow" pkg in the dually that wasn't offered in the SRW. Then in 2013MY the DRW got a different front suspension and a slightly larger rear axle ring gear. 2014MY the 3500 SRW got the same front suspensions as the dually, but I don't think it gets the larger ring gear.