Idle Problems

My gf has a 2000 GT auto, and within the last year, it's been giving her some fits. When she pulls up to stop somewhere, the car's RPM will dip, almost to the point of dying (it has died a couple times), and then the RPM surges up past idle, then settles in to where it should be. If it was a stick, it wouldn't be a HUGE deal, except that since it's an auto, the RPM surge causes the car to lunge forward, which if she get's stuck in a tight space, she'll hit the car in front of her. She's rebuilt the tranny, but it didn't help. I figured the best place to turn for advice on how to fix it would be you guys It's gradually doing this more and more, it's probably up to doing this lunging thing about 80% of the times she stops. Please help!

I'll be running the tests this next week, but I can rule out the tranny problems because when she pulls in to a parking lot, to keep it from surging forward and hitting a car, she pulls in to a spot and immediately puts it in park and it still has the RPM drop and surge. Thanks for the help, I'll post back with what I find out!