I live in Ontario Canada. I have a 2000 Pontiac Montana minivan with 101,000 km. In September/04 I took it to the dealership because I noticed, on occasion, i.e. not always, that the auto transmission would have harsh, very noticeable shifts and one could hear a whine from the engine/transmission during acceleration.
It took me a month or more to bring in the car because not always would the problem occur. And when it did occur it would often stop if I turned the car off and then restarted!. Eventually I was able to drive it to the dealership during an episode :) and get a rep to drive with me. They diagnosed it as a problem with a sticking pressure control solenoid with the sticking due to sediment build up (I am looking at my September/04 invoice). So almost $700 Canadian later it was fixed.
It is now March/05 just over 6 months later and 12,000 km more and the same problem has reappeared! :( It wont take me as long this time to bring it in as I recognize the same symptoms.
I did a bit of googling and found this appropriate TSB # 00-07-30-002B
Thanks for your experience.