dropping out of overdrive

2003 GTP drops out of OD after about 20 seconds. Anyone else have this problem?

Sounds like you might have a TC lockup solenoid going bad perhaps..Any other issues besides the dropout? Is this the first time this has happened? Check engine light come on or anything else when you experienced this? In fact, regardless of whether it threw a light, there may be a code stored in the PCM for the problem you had. I'd stop by an automotive shop & get them to scan for any codes first before replacing anything..

Have you checked your fluid or has it been changed in a while. You might could drain it, put a new filter in and add some trans-x or lucas to it when filling it back up that might help you out some but not really sure.

intermittent slippage on take off. No lights,no codes.
Just serviced tranny.

Drops out every time and at same interval.

what RPM range? How sure are you that the shop did your tranny right? Do you have enough fluid? Perhaps the t/c is bad. If it really is slippage, I doubt that it would be anything electronic or vacuum related.