I have a 2001 Pontiac Grand Prix GT with a 3.8 V6. I just got this car in Sept. 2008 and had the transmission rebuilt in October for worn shift plates. I recently had my service engine light come on and the ABS light along with my traction control no longer coming on. My car has started to hesitate when taking off from a stop and one day it was jerking extremely bad going down the highway. The jerking stopped before I ever had anything done to this car and has not happened sense. It does however seem to shift a little harder from fourth to fifth gear than it does in lower gears. The scans say that the transmission is fine and it never does this when I take it to the shop. The cam sensor was replaced and so far the ABS light is staying off and the traction control is working. My service engine light is still on and reads for a cam shaft sensor. I know nothing about cars and going strictly on what mechanics tell me. He told me that in this particular motor there is some sort of magnet involved with that sensor that rarely but sometimes comes loose. Said the whole front of my motor would have to come off to get to it and check that magnet or replace the sensor whichever is needed if not wiring. This could run over $1000. Has anyone had this problem or know anything about it? I would greatly appreciate any advice.