["The 1/2 ton is narrow at the front and wider at the back, tapering the whole way. The 3/4 ton only tapers from front to about the middle of the cab, from there back the rails are parallel."]
I believe that is what I said...
Wider at the back, front suspension is heaver and a bit different. I have dealt with those issues on my 3/4 ton and admit it is harder to find correct parts as most are designed for the 1/2 ton; but it can be done.
