I've been having transmission issues when using the tapshifter in my 08' Grand Prix GXP, I know it's a 4T65E so I'm not sure if this is the right place for the post but anyways...In tapshift mode if you run 1st gear up close to redline and backoff without shifting the car will drop into neutral and the RPMs flatline. When I re-enagaged the throttle the RPM will climb still in neutral and the car will then slam into gear. Another odd thing happening is when in 2nd at highway speeds if I do the same thing, run the car higher in the RPM band and backoff, the RPMs fluctuate quite a bit, jumping 500+ and coming back down and repeating as the car eventually slows down. Last but not least dropping the car into 1st at or around the rev limit (41mph) the car will drop out of gear much like scenario 1 and the RPMs will flat line, if I rengage the throttle the same thing happens, slams back into gear etc. Any ideas on whats going on?

Couple of things...before this started happening I had made an appointment at the local dealership because of a tapping noise on start-up. They isolated the problems to the lifters and they are being replaced as I type this. Could the lifters somehow be tied to the transmission problems?

Also, for some dumb reason I decided for the first time to throw some octane booster in my tank after already filling it with premium gas. Not too longer after, probably less than a day later this started happening. Add this to the fact that I already live at 4500 ft and the octane requirement is lower. Could I have thrown the timing off to cause something like this?

I checked the TEP site, got nothing. I've tried on a few different forums, nothing. Any input would be appreciated.


Thanks