I bought 88 GT vert few months ago thats super clean and has a jasper crate motor and whole cars stock. I put msd cap,rotor,coil and new motorcraft pkugs and bbk cold air intake with speed density adapter cuz its not mass air car. But every once in a while when it get on gas hard and shift from 3rd to 4th or 2nd to 3rd it will backfire out of exhaust and in worried its running lean cuz of more air flow and dont want to damge brand new motor. Question is doesnt anyone have any advise what could be causing this. I was thinking of getting adjustable fuel pressure regulator and gauge for shrader valve to monitor or give more fuel if that would help. Any input would be helpful