i have a built up 5.0 and i have been having problems getting it tune it seemed that i would get it running perfect and the next day i go to start her and it running like crap so i replaced my o2 sensor and fuel injectors! and i still runs like crap and is not firing in one cylinder i can tell by the spark plug and the way it runs! i had a guy make a tune for me and i not sure if its his tune or what but this is driving me crazy and advice would be great i at the point where i wanna rip my hair out