Hi, I have a 2001 Grand Prix GT, and a few weeks ago, I was driving and it said I was going 80 when I was only going 40. So I stopped and put it in park, waited a bit, and it seemed to work again. Today, I started the car and pulled away, while the speedometer did not work. The car also seemed to jerk around and the rpm's were going up and down slightly. When pulling away, or maintaining speed on the highway, it just jerks and feels really bad for the car. After a little bit, the speedometer worked again, but the jerkiness was still there and the car seems like something is not right. I am worried. What would be the problem? Thanks.