Ok im not sure if its the gear or not but my bro's 07 Grand prix Base has been lately having this jolt from the car a few time when he accelerates from a stop. when we stop at a red light then start going the car move forward a little and we can hear the engine getting louder and then the car like gives a great big jolt and then starts going. I don't know how else to describe it and we don't know what's wrong with it. the car hit 100k mile just 2 days ago and the big jolt that happens has been going on for a while now but we did not get the car a big exception yet but we will need to, you guys know what's wrong with it?