Gm only gives the dealer the ability to program the truck with the possible tire combinations available for that truck... meaning is it possible to get a truck with that engine and chassis with that size tire?? if not , then gm cannot program the vehicle... you also have to program the abs and pcm separately... some dealers just program the abs, which is much more lenient, and the shift points and Speedo are still wrong...If you find someone who deals in tires, you may be able to find a match of circumference of tires between what you have and what is available.... as for aftermarket, I don't know how they do it... must kinda be like hacked firmware for a dvd player or something....probably works, I just have no experience with it... Bobo
P.S. If you plan on leaving it as it is... I would try to have the dealer program the abs for the brakes.. the small change in speed may have a dramatic effect in how the abs works... I know it's a small speed change, but with thousands of pounds here it wouldn't take a lot to throw a monket wrench in the works....
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