I had a collapsed electrode on one of my spark plugs.. tach read low .. gas mileage was lower but it ran great and showed no codes .. I had a tune and thought maybe it’s the tune , had the tuner check it and do some adjustments ... didn’t matter nothing changed. I had replaced the plugs just recently at that time .. ran the truck for many years .. took a long road trip last year .. ran fine until the day after started home from the trip .. I started feeling a very slight miss at low speeds but cleared up while cruising at highway speed .. figured when I get home it was time to check and change the plugs again ,, also was showing codes . I pulled the plugs and found a collapsed electrode on one .. changed them and to my amaaaazment the slight miss was gone . Tack was smooth reading and the RPM was up a bit , normal spec, I also gained the mileage back that I lost .. went from 10.4 highway to over 14 highway .. moral of this is when you change your plugs make sure the gap is correct and don’t unintentionally bump the plugs when installing them.