Im looking for some help with my sons car. He has a 99 Grand AM GT with automatic trans with 99,000 miles. He has been having issues with the trans slipping when engine is hot. If he is driving the interstate for the most part it is just fine without issues, but if he is driving city the trans will rev a little before shifting and slip. then when parking and running into stores, get gas or go to the bank, he will start it up , place into gear and it will slip going into drive.


Here is the catch, this is the second trans in this car. The first one did the exact same thing as this one. The transmission that was just put in, was all gone over from a tranny shop and had 65,000 miles. the reason we had a tranny put in was they said the valve body had a crack in it. So we chose to just replace it with a used one that had warranty.


Now that this one is doing the same exact thing, im starting to believe its something else.
Does anyone have any idea what it could be and how to test it ?


Note it never once threw any codes.


Thanks you Shawn

Need a better timeline.....

Car now has 99K......

The replacement tranny had 65K on it.....you said it has a warranty,,,what is it?

What was the mileage on the car when installed(also the date).....

So they were saying that a cracked valve body was causing the original slip?

Assume this is a 4t45E.....

Has the vehicle been driven by the people diagnosing the car, with a scan tool, taking a snapshot of the data while driving? Did they check slip data? Did they check fluid temp data? Sure no codes were set?

The "symptoms" of the "new" tranny are the SAME as the old one?

When a new transmission is installed, the lines and the cooler in the radiator have to be flushed,,,,was this done?

I forgot one question:

You say problems arise in traffic........let'* say you have been driving on the highway for awhile, and you exit the highway, come to a stop......now get back on the highway, as you accelerate from a stop, is the slip condition there?