2001 gt recently started jerking, at highway speed .and the speed odometer would go up to 90 mph when your going 55-60 mph it did this a few weeks ago and i replaced the icm, crank position sensor, and different coils. this seemed to fix for a while, but now i am back to square one. i do not want to throw more parts at it ,without more knowledge or $$! any body had this problem or a ideal what this might be thanks.