Might be. Are you running an SCT tuner? I asked Hemifever if he could raise the TC lockup in OD. He said, "Sure" and bumped it up to 50 mph.

 

LOL! Yeah, I don't see any unless somebody quotes him.

 

Oops! DP

 

these damn things do shift into OD at too low of a speed, about 40-45 mph. they also have an extra feeling of a shift, which is the torque converter locking/unlocking.

its my understanding there are 2 versions of pcm programming related to torque converter lockup. the original one is 1-2-3-tc_lock-OD. i have this and it gives a little shudder at low speeds with lock up. its also a dog at low speeds with bigger tires. the new and improved is 1-2-3-OD-tc_lock. with the new one, when OD is OFF, then tc_lock is also OFF.

i've considered having mine reflashed, but i think its an irreversible decision.

to answer your original question, the tire size is in the pcm, as revolutions per mile. i don't think gear is involved.

 

My truck shifts into third gear at 41mph. And shifts into overdrive at 48mph. I like this very much. Even if I baby the pedal, it will just stay in 3rd gear, and I can keep my powerband.