I agree, any effects of an oil overfill should have shown up long before 1,000 miles were put on the truck, that said, if it happened to occur along with the recent cold spell most of the country is experiencing, the effects of the over fill may have been attributed to the weather until some damage has been done. 3 quarts of overfill would probably put the crank in the oil while is was spinning. Your son didn't drive through high water did he? It may not have been extra oil in the crankcase.

The way it sounds to me, I would want to verify there are injectors that are hanging open. The oil over fill could also be gas in the oil.

If it was running the same way after the dealer service as it was before, they obviously didn't fix it. Stand your ground, take the battle as far as you need to go. is the oil level correct right now?

I suspect we are not hearing the entire story here. Gene