I recently picked up a 2001 Silverado 2500 with a fresh engine around 60k and the truck has little of a rough idle, she runs fine but when is not moving you can feel little miss, the service engine soon light comes on after 70+ mph which it goes away if I slow down and that would be the misfire, the other two codes are about lean somewhere. I did my research and it says it might be the plastic shim that wear out with time and or the sensor itself, now I was going to do a full tune up within the next couple of days which I was going to change plugs, wires, and filter. The day after I got her I got the oil changed, changed air filter, cleaned mass sensor and a full tank of 91 and a bottle of Lucas fuel treatment. Should I do the full tune up first and see if the problem goes away? I do a little exhaust leak that I will get fixed next week.