Hey so i have a 2000 Pontiac Grand Prix GT and everytime i am driving and i accelerate to hit about 55 mph my car literally starts to jump back and forth, and the tach jumps from 2000-3000 rpm. to fix it i can either keep stepping on the gas for it to adjust itself or i can let go of the gas for one second and then step back onto it. i have no idea what is causing this. any help is appreciated.