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I took this from Allison's website:

Q. Speedometer / Tires - What effects will big tires have on transmission operation? A. The TCM calibration is based on factory tire size and rear axle ratio. Changing either of these parameters will have some adverse impact on transmission operation, including features like grade braking and shift stabilization. For instance, we have noted that when P285 tires are installed that the transmission generally does not shift to 5th range when towing heavy loads.

My question, can my dealer change the TCM calibration and the speedo calibration to compensate for my new 285's or is the TCM calibration a fixed thing / and is it necessary?
 

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They might be able to...see if they can reprogram the TCM with TIS2000, but when it asks for a VIN, input a 3500SRW's VIN. That way it will program it for 265 tires (3500 single rear wheel's get 265s)...may not be completely fixed, but it will be better. I dont know 100% if this will work...better to get an oppinion from Mike or Eric before actually trying it....

--Ben
 

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I talked to a guy at a GM dealership about putting a westers in my truck. And in our conversation we got talking about the ally he claims that he can adj the shift points slightly. Don't know how but I am going to put the westers in and he said we will "play with them from there"
 

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No he cant. Everything related to the trans is in the TCM. Which nobody (except Allison) has the power to program or control...yet...

another reason why raising the rev limiter with a tuner on a Allison equipped truck is pointless...it doesnt do anything except allow you to rev your truck to 4 grand in PARK! :)

--Ben
 
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