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Old 03-06-2019, 09:18 AM   #51 (permalink)
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Join Date: Apr 2012
Location: Evensville, TN
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Deep Blue - '94 GMC Suburban K2500 SLE
90 day: 23.75 mpg (US)

Griffin (T4R) - '99 Toyota 4Runner SR5
90 day: 25.43 mpg (US)
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I am surprised by the cost of the Allison swap. I have the 5 speed Allison 1000 in my 2001 2500HD behind the 8.1L big block. All the Allison 1000ís are six speeds, the sixth speed just isnít enabled in the 5 speed versions. I have heard of people enabling them, but I donít know about cost. If you are replacing the torque converter anyway, a 2006-2007 Chevy/GMC 2500HD Pickup with the 8.1L may be a cheaper source for a 6 speed Allison 1000. They donít dip the 8.1Ls in gold like they do the Duramax and low mileage units can be found. (Note the Suburban/Avalanche with 8.1s and the pickups with 6.0 do not have the Allison, despite what sellers list them as.)

If gearing is the only thing holding you back from a manual, you can put together a .648 OD NV4500, I have one not that bad of a job. Got about 3500 miles on it behind a 6.5L, no issues.

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