Looking to buy a 2005/2006 Dodge Diesel 3500 , 4x4 with auto trans. , and 3. 73 rear end. Was looking for specific payloads/towing differences in the 3500 series with a short box SRW... long box SRW and long box DRW. ?? Or are they all the same given the above parameters. ?? Or another way to word the question... is what am I giving up if I forgo the dually. ???