I realized very early that I was never going to be able to speed shift my 2002 Cummins 6 speed. I did one of the BD short shift kits to no avail. The problem is, of course, the manual truck transmissions internals that are designed to go 200,000+ miles have to be so strong and heavy to stand up to the brutal abuse of a clutch in a heavy vehicle with huge torque output, that they simply cannot change gears quickly. My 2002 QuadCab 2wd weighed nearly 7,500# empty. The only transmission that could survive would be a race prepped automatic that has the cushion of a torque converter. If you could cut the weight of the vehicle down to 2,000# you could probably have a car 4 speed (like a Chrysler) handle the job, but the big diesel engines themselves weigh well over 1,000#, so how can you build a complete light weight package around that?