You could try a different pcm but I doubt that is going to fix anything unless you are throwing driver and shift solenoid electrical codes and it is not commanding the solenoids as they should be. There are a few things inside the transmission that can cause a 2nd gear start either cold or after being warmed up. Also- I have ran into bad new aftermarket shift solenoids that once warmed up caused the car to want to start off in 4th gear after driving in D range for a while and work fine once cooled back down. The shift solenoid output function of the pcm is simple and if there is any electrical fault there should be a code, doesnt matter if it is the correct pcm for your car and you could use a 98-02 GTP pcm and it will work fine. If there is a gear ratio problem it would throw an incorrect gear ratio code, especially if the pcm was just reflashed back to stock at the dealer. Have you tried to manually shift the car back into 1st when this happens to see if it works ok or does that not help any?
