I suggest going here and do some reading:
6.2 and 6.5 Diesel Engines | The Truck Stop
I am a member there also.
I have a 96 and 93 6.5 diesel. am fixing the 96 up for sale but will be keeping the 93.
I installed a Gearvendors OD unit, have the auto and 4.10 gears. at 65 I am at 2000 rpm, which is the ideal rpm for these engines.
I plan on putting a short bed and to shorten the frame and I want to put in a 5 speed and 12 valve Cummins.