Hi, I am having a surge issue when I hold at 35mph. About a 200 rpm jump. Also when I left off the gas, and switch to manual and keep it in 5th, the rpm jumps up and down as if it's down shifting but it's not. The engine and the light jerk feels just like it would when it down shifts. I have replaced the pcv, fuel vent valve, the fuel cannister. My mechanic can't figure it out. Any ideas?