Who recommended auto lites?Could the spark plug gap have anything to do with the mileage. I just changed the plugs in mine. Plugs I removed was gapped at .034. Put the recommended autolight plugs in and gapped them at .030. Mileage went from 17 to 15 (all highway miles). Thinking about pulling them out and gapping them a little bigger. Oh I didn’t mention I have a 13 screw with 3.5 ecoboost
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All recommended plugs are these are stock motocraft or NGK because NGK makes them for Ford.