4spd vs 6spd Allison question.
If I can find 2007 Chev/GMC 3500 with the 8.1 I would like to think about picking one up. I drive my 2002 by the tach, 65 mph=2100 rpm. That seems to be the sweet spot for best mileage. I know I am...
Forum Discussion
trail-explorer wrote:ramyankee wrote:
Driving the 6 spd might give me a slight increase in mileage because of the 2 extra speeds.
Extra 2 speeds compared to "what"?
All 8.1 engines were paired with the Allison transmission, which was either a 5 speed or 6 speed. 6 speed was 2006 and later I believe - at least that was the case on the Duramax / Allison combo.
2005 and earlier was 5 speed.
Correct. On the 8.1 gassers the 6th speed was introduced in 2006. Prior years had the 5 speed. The difference was rather inconsequential.
The Allison was the only transmission available if the 8.1 was selected on the order sheet.
