I have a 2003 Chevy Malibu 3.1 V6 with the 4T40-E transmission. As I was leaving my friends house I put my car in drive and it was working fine. She lives on a gravel road and by the time I got to the highway I noticed it shift really roughly. So when I got to the stop light I put my car in Park and back into Drive and the car slammed into drive. Usually you can't even feel it. It continued to shift roughly the whole way home. When I got home I also noticed my transmission was making a sort of light grinding noise in Park, Drive, Neutral, and Reverse. I turned my car off and on right away and it still did it. Then I turned my car off and waited about 5 minutes and it didn't do it anymore. Smooth shifting and no noise from transmission. That happened yesterday evening and today I drove it for about 45 minutes and its working great. I'm thinking that it doesn't have to do with a mechanical fault in the transmission, but rather a sensor or something else that is commanding the pressure solenoid to do full pressure. Does that sound about right? I know there are a couple of sensors that can make the transmission default to full pressure. I scanned the car and there is also no codes set.
It is the IAT sensor. almost positive it is the issue, weven without a check engine light for it. It normally fails full cold. like -32F.