Always wondering about someone else turning wrenches on my vehicle the first thing that I would check is that the spark plugs are torqued to the right specs and that the threads for the #6 cyl. are ok. Be very carful not to overtighten the plugs since they are threaded into aluminum. Other than that if you have an internal engine problem you could take the instrument cluster out and pull the bulb for the check engine light and ship the truck.