I bought my GM at 82,000 miles. It is now nearing 140,000 and was starting to idle a bit rought and miss a bit more than I liked. I thought maybe the original plugs could still be in it and they are rated to be changed 100,000. I pulled the plugs and to my surprise they were the E3's. I swapped them out for Autolite Iridium as AZ had a nice rebate on them. Everyone says that Autolite makes Motorcraft. The car runs much smoother and feels much stronger via the butt dyno. The missing has completely stopped. I used to be able to make it miss in hot weather on small hill climb under light load trying to accelerate very lightly. Not enough to make it downshift but put a light load on it and a missing it would go. Bucking. Now I cannot seem to make it happen. Wish I had checked these sooner but beter late than never.