I use Autolite 3923's in my truck. You can get them for $3.00 for 2 plugs in a pack at Walmart. They are one heat range colder and will help with pinging if you have any. My truck runs great on them. I have tried other plugs including NGK and 3924's but I always go back to the plain old copper core 3923. It has performed the best in my 3.9. I change plugs, my distributor cap and rotor button with Napa part #'s MO 26 and MO28 brass contact cap and rotor at every 20,000 miles, I change my plug wires out every 40,000 miles. I use the Belden Premium wire set from Napa, about $36.00 here.