99 GTP Tranny PROBLEMs!! HELP!

Okay, this is how it is. I got my 99 GTP last year with 70,000 miles or so on it. About 3 months ago, I changed my tranny fluid/filter. Since then i've noticed my tranny wants to hold on to gears at high RPM's. For instance, if I "gun it" while in first, my car won't shift when it should, whether its in PS or not. IT does help to have performance shift on, but it will seem like its in between gears for a second or so before it shifts completely into the next gear. I now have a 3.25 pulley / new PCM in the car, so im not sure if that made things worse or not. But any helpful suggestions on some things that might have been done wrong on the transmission fluid/filter change or what not would be great. ( no i didnt flush the thing out, just drained and changed fluid.)

Check the vacuum modulator. The Haynes manual I have does not show exactly where it is on the 4t65-e but that is where I would look first. You have classic signs of a modulator valve that is not working properly. When you accelerate the vacuum on the engine drops and a bad modulator or vacuum hose leading to it would cause it not to want to shift properly. Second, make sure the fluid level is proper. If it is too low the line pressure will not be great enough to allow it to shift properly. Sometimes you need to add a little more than the fluid change capacity indicated in the manual. Hope this helps!

Check the vacuum modulator. The Haynes manual I have does not show exactly where it is on the 4t65-e but that is where I would look first. You have classic signs of a modulator valve that is not working properly. When you accelerate the vacuum on the engine drops and a bad modulator or vacuum hose leading to it would cause it not to want to shift properly. Second, make sure the fluid level is proper. If it is too low the line pressure will not be great enough to allow it to shift properly. Sometimes you need to add a little more than the fluid change capacity indicated in the manual. Hope this helps!


Hey thanks a ton, all good information. But one last thing, how could i go about fixing that exactly if it is the problem? ANd yeah, when i looked at the manual, it was like I took more fluid out than was put back in. I did check the fluid level to make sure, and it seems to be at the right spot, so maybe ill add just a little more. THank you :)

The vacuum modulator on the 4t60-e is located on the top of the transmission. Should be in the samp place on teh 4t65-e. It is simple to change and is located on the radiator side of the transmission below the crossover pipe and has a vacuum line connected to it. Just remove the mounting bolt, and pull the modulator out. Then with a small hook or screwdriver remove the O-ring. Then take a small magnet and remove the modulator valve from the hole. Replace in the reverse order with the new one. Put in a new o-ring, don't reuse the old one.