My check engine light came on after towing a boat and a uhaul a few hundred miles. My truck has 70k miles on it so its not suprising. The symptom my truck was having was when letting off the gas the truck would jerk forward and backwards. I just got the clutch replaced so I thought maybe there was something wrong with that. I thought I better see if the check engine light was the problem first because thats usually some cheap sensor that went bad. So I bought a diagnostic computer from Auto Zone and hooked it up to the OBD II port. It came back with error Code P0121
TPS / Pedal Position Sensor A
CKT Range / Perf
So after doing some research online, I went to Napa and bought the OEM TPS for 49 bucks with tax, Its attached to the air intake manifold on top of the 5.2 L engine and walla! That solved my problem. The truck is riding like brand new.