I recently purchased an 06 Grand Prix GXP. It has 4T65E high performance street/strip rebuild with reman torque converter and 3.29 gears. It also as a Tru Cool 4711 Cooler. The transmission was installed by Triple Edge Performance in Indiana. The previous owner had another company do the TCM reprogramming though. I drove the car home from her house, 137 miles. When I was almost home it sorta jumped gears. Did it for a second so didn't put much thought into it, thought it was just me making things up because it had been a long day and was late at night and I was tried by this point in time. Anyways, the next day comes and it drove great all day. Monday rolls around im drivinf around all day, then it starts this strange bucking almost like thing. Cruising through town at 30 mpg it wanted to shift to 4th but then kept jumping back and forth between 3rd & 4th gear. I got off the throttle and then back on it and it stayed in 4th. I keep an eye on the transmission temp and as soon as the temp gets above 180 this strange bucking starts. Not all the time, and only while cruising down the road. Whether its at 30 mpg or 75 mpg. It never does it while coming off of a stop. And it doesnt do it at all if the transmission temp stays below 180. Once the transmission temp reaches 180 it does this bucking thing, even if the temp comes back down to the 160 range it will still buck until the transmission has completely cooled down. Ive even put the car into manuel mode and made it shift to 4th and the car will still buck itself in & out of 3rd & 4th. Here it is 3 days later and it is still doing this bucking thing from time to time after the temp going above 180. I am currently talking with triple edge performance to see what I should do, but what else should I be looking at? Ive never experienced this in any grand prix ive ever owned.
