my stang is running like a pos sometimes
 

I got my new motor in and it runs nice when it wants to the last couple days its been acting up mostly when im driving on the hwy then it started doing it in town it will spit,sputter,bog and make poping noises out of the intake at low rpm if i get on the throttle it goes away one minute it will do it alot the next it would run perfect sometimes for an hour. It pops like its out of time but it cant jump in and out of time could it?anyone got any idea what it could be thanks

its a 5.0 with gt 40 heads and intake mass air conversion