I was wondering on this whole 2500 3500 thing I have added the 3500 leafs and springs to my 2500. the only thing diff I may do is add the dully wheels if needed. my truck is the HD version of the 2500 2007 6.7L. what I would like to know because my friend owns the 3500hd and ive looked it over compared to my truck is why such the differece in towing and payload specs is it just the springs and dully wheels. Is it a safety thing aposed to weight capacity for the trucks parts because the parts and frames are the same to the naked eye.