Everyone always says that. To me it seems like the 6 speed 68rfe would be better than the other allisons. Not sure about how the new allis are.
I had the 6spdAlli behind mine. Shifts were smooth, and the pattern worked well with the Cummins...kept it right in its power band. That truck had a LOT of get-up. It would wipe out a set of rear tires in 17,000 miles, and thats not from hot-rodding it.
Only reason Im not driving it now is the regenerations were so out-of-hand....every 50 miles. The stink and potential health issues (nobody could tell me yes or no, so I opted on the safe side) from the fumes finally became too much of a problem for me. If I could have deleted the DPF, that truck wouldve been flat-out perfect. Id still be driving it.
Mechanics changed out EGR valve twice, the turbo once (didnt need it but we were trying to solve DPF issues) and a host of DPF pressure/temp sensors, but nothing else. Thats stop-n-go, 0-100% throttle 120x a day in a 10,000lbs truck on 185mile route...very severe conditions. The 6.7 was quiet and ran great.