Faulty Pressure Control Solenoid, GM knows about it, there are TSB about it. Harsh shifts when hot. The best and cheapest thing to do is call GM and complain. Their number is 1-800-222-1020. These transmissions are known to be defective but have yet to be recalled. I called today 6-21-2010. Ask for it to be recalled. If they get enough calls they will. Maybe. They acted like they knew nothing about it which I do not like being lied to.