Well I am back to having conversations about my project (the '06 LBZ is still in the garage!). I just talked with a used engine/transmission reseller here in the local area and he has a number of different model Allison's in stock. I have been looking at the 2550 as it has the lower gear ratios in 1st and 2nd and the parking pawl. Allison didn't allow parking pawls in new units if they were over 22,000 lbs. Mine is 14,000 plus an tow vehicle which could take me up to 18,000 lbs gross weight.
The question of the day is whether I should go with a 5 speed or a 6 speed. With my present rear end and wheels, which I will not change, the 5 speed would put the Duramax LBZ at about 2200 rpm at 65mph. The 6 speed would put the engine at about 1900 rpm.
To all of you Duramax folks that run with loads in that range a lot of the time, where should I target my RPM? Reasons?
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