Valve cover gaskets are a very common leak and you have the right symptoms. I have the same engine (same year and mileage too) and have just finished changing the valve cover gaskets. Be sure the half circle part is seated and be sure to use the FIPG where it is required in the FSM. It is a bit of a chore to pull the air intake to get to them so I would consider other things that you might want to do while you are in there. I pulled the fuel injectors and had them cleaned while I was at it.