Mattyg717 
I'm new to the Grand Prix world, but I've had transmission problems with Chrysler/Dodge that turned out to be a $25 part, a transmission speed sensor (input or output, I can't remember now.)Originally Posted by Mattyg717
Symptoms: Starts normally, start driving, going down the road the transmission will slip, then recover. (Basically, if the sensor can't detect shaft speed it throws the transmission into neutral.) After a few more times of this, the transmission goes to "limp mode" where it won't go into higher gears, but otherwise operates fine.
I don't know if this is applicable to Pontiacs, but just throwing it out there as an idea, because it's been a cheap fix for me 3 or 4 times on different Chrysler/Dodge vehicles.
