Just got my rig back from the dealer. It was in for the steering column shaft rattle and the tailgate cable recall. They lubed the steering column and the rattle seems to have gone away (for now?).

While I was there I asked a few questions:

Q: if I put 265's on instead of the 245's will that void my warranty? A: Not sure, keep the 254's around and if you have to put them back on then that's what you have to do. Additionally, they commented that the Alli requires that only 245's be used. I'd never heard that before.

Q: Have you been getting many injector replacements? A: A few, but not many. However there was a guy in the shop with dealer plates that was in for injectors.

Q: How much to hook up a tech II and check the balance rates on my injectors (I'd like to know if they're on their way out before I'm stranded)? A: $88, but he didn't seem to think it was worth the time or money, commenting that when they go they're gonna go all the way and that checking balance rates isn't going to tell you much.

Q: How can I tell if my ECM needs to be reflashed? A: It would come up on our computer and we would have done it automatically next time into the shop.

So, there it is...:D

I believe I read that the 3500s come with 265 tires from the factory. Even though your speedo would need calibrated, It seems like it shouldn't be a problem.

what would larger diameter tires do to the allison? is it something that can be fixed by changing the 3.73 rear to a 4.10

I believe 265s are about 4% taller, so for the same road speed the engine is running 4% slower. Unless you tow huge loads constantly, I can't imagine that you would need to go to a 4.10, which would be a 9 - 10% change. As far as the effect on the trans, I don't know of any. GM may not want bigger tires, because with the effect of a lower numerical rearend, the engine/trans could have to lug more.

dealers say 245 because that is what is programmed into the TCM for shift points, also maps to the torque curve of the engine. That said, I am running 315s with the juice and no adverse affects, even towing, for 15K miles. I have towed as heavy as 12K, no problems.

I had factory 245's until I put 265's on and noticed that the speedo is more accurate with the 265's than it was with the 245's.

Tim

ah..another uneducated dealer....

dealer put my 265's on for me before I picked up my truck new