I am planning to get a tune-up soon. A guy at Advanced Auto Parts recommends AC-Delco Iranium plugs for my 4.9L, but the mechanic I might go to says AC-Delco Platinum plugs are better. Also, the shop suggests cleaning my fuel injection system, even though I normally run Premium octane and put injector cleaner in every so often. My last two tanks of gas have been mid-grade, however. Is that likely to foul my injectors? And what about a K&N air filter?