check engine

Good afternoon, ill try and give as much detail as i can on this and TIA for any advice! A little info about the car - 2018 42k miles owned since 9k. No prior mods were done to the car except PPF Stock tune Stock motor Roush CIA without tune (installed 2+ years ago) 2 12" subs connected to one...

About a month ago, I purchased a 2017 GT CPO from Dallas. About a week and a half in I was already having issues, but the worst of them all was the misfires. Codes are P0316 and P0308 which is misfire at startup and misfire on cylinder 8. The first trip to the dealer, they swapped the plugs and...