It's a 4" down pipe and back to just behind the cab, then 5" from there out to the tail gate, with a 5" Magnaflow muffler that is 4" straight through.
I probably won't be driving to Huntsville, I just found a bunch of stuff to do/redo before I put the cab on.. I'll explain and enlighten in a month or so, stay tuned. I may drag it down to Huntsville as is though.