Ive noticed that my car shifts into 4th, or overdrive as im accelerating at 40+mph, its kind of annoying. I plan on getting the transmission tuned at a local shop but im alittle strapped for cash at the moment. I was wondering if shifting my trans myself will hurt the tranny?

 

It won't hurt shifting manually. It is supposed to shift into OD if you are just cruising. It is not supposed to do that at WOT.

 

you could allways just put it in regular Drive, then it will only shift up to 3rd

 

will running the car in just regular drive until third and waiting to shift into overdrive(forth) at a higher rpm actually give you a better quarter mile time compared to just leaving it in overdrive the entire pass down the track, or is that bad on the engine.

 

The car will not shift into OD at WOT, you can run it in OD or D and it will be the same. Also there is absolutly not performance benifit to shift a 4L60E manually, the sift points are calculated by speed, rpm and throttle position.