Just to clarify, is the '01 5.9 a 360 gas or diesel? If it's diesel then swapping sheet metal would be the easiest. If it's gas (which I'm thinking it is) it still might be the easier way to go. You could swap drive lines, but the 2500 has a heavier, stronger frame. If the only thing wrong with the 2500 is the sheet metal then swapping bodies might be the way to go, you will get the heavier chassis. Just my opinion anyway.