Price. 73-87 Chassis are cheap,They are cheap to get, modify and repair. 88+ are not. I have played with the idea of finding a 88+ 3/4 or 1 ton 4x4 to put a 46 1.5 ton cab on (still working with the County to get that truck). On occasion I find the 88+ chassis in the junk yard or cheap on Ebay. In fact the 88+ have a straighter frame rail under the cab than a 73-87 which makes it easier to swap an older cab onto.
