Ok this is my first post on here too. I have an 05 grand prix 3800 and mine is kinda doin the same thing. It drives fine and then at random its like it comes out of gear and just revs up without moving. Then when I come to a stop and try to take off the car shakes like its gonna die but revs up and doesn't move. I actually just finally limped it home and got into my driveway and I couldn't move, I didn't have reverse or drive just reved up. I turned the car off then back on and it shifted itself into every gear. I read to unplug the MAP sensor but I kinda was looking for other possibilities. Thanks.