There was a day that the 2500, and the 3500 was the same truck , except the rear spring pack , sounds like now there is a difference in axles , and I would assume brakes? That’s possibly about it ? I know a lot of tires are the same E rated @ 3640 lbs @ 80 psi . I get kinda of a kick out of the weight police here . My big concern would always be tire rating . These truck are still the same motor, body etc , what the rear axle burns up on a 2500 with a 15000 GVWR fifth wheel,and doesn’t with a 3500 ? So you upgrade the rear springs ,now what kind of issues will you have with the 2500 , just asking , I’m sure the weight police will answer.