have u cleaned the maf, change air filter. im sure u have considering its a new motor. someone used to make headers fo the 4.0 and i think comp cams has a cam. ive been considering those two upgrades myself but figured id wait til i gotta rebuild the motor. im not hoppin up a 11 year old motor with 280k on the clock when it runs fine gets great mpgs and doesnt leak or burn a drop of oil. heck i even recently cleaned my maf and iac and they looked cood considering its been at least 5 years since i did it before. ran seafoam through it and it didnt smoke a bit. other than my 300s ive had in my f150s this has been one of the most reliable gassers ive ever had. sorry to hear u havent been so lucky