2000 Grand Prix Jerks When Shifting

I have a 2000 Grand Prix GT with the 3.8 liter v6. It has 108,000 miles. I have noticed recently the car will jerk/clunk when upshifting-even when I'm easy on the throttle. Once I shut the car off and start it up again, the problem goes away. I checked the tranny fluid and it is fine. I've noticed the Track Off and ABS lights on every now and then but not every time. Any ideas? Thanks!

There is a known issue with the PCS (pressure control solenoid) in the transmission which will cause harsh shifting. You could try some Seafoam or Lucas trans additive to see if it free's it up, but I doubt it will help. Another trick that has worked for other forum members (although usually only temporarily) is to unhook the battery and leave it overnight.