I too would love a 6 speed. i have even looked into putting a 68rfe in when my current trans dies. It isn't cheap though and i am sure their would be many growing pains.
My 91 cummins was a stick 5 spd (dual disk clutch) with Gear vendors OD (essentially a 4 spd with two od gears, similar to the 68rfe), loved that trans. setup (except it wasn't the fastest shifting thing around).
http://www.transmissiontuner.com/68RFE-Tuning.html
My 91 cummins was a stick 5 spd (dual disk clutch) with Gear vendors OD (essentially a 4 spd with two od gears, similar to the 68rfe), loved that trans. setup (except it wasn't the fastest shifting thing around).
http://www.transmissiontuner.com/68RFE-Tuning.html