Roy is right. While the valve covers off have the valve clearances checked. They are Shim adjusted and people over look adjusting the valves, chances are only one or two may need to be adjusted but with the covers off nows the time to do it.
it pays 3 hours in a shop. you need to remove the upper intake to gain acess. it is very involved for doing it at home. i suggest calling around for pricing to let a shop do it for you. try our estimator tab at the top for a list of shops in your area.