help help help

[vash21]

hi i just got my my sr red top running. but i m having some problems. its running like a dream when i first start it up. idle is right pulls damn good when i get on the gas. but the problem is when i have been driving it for a while it will start sputtering when i get into boost.....you can hear pop a out of the exhaust. i have changed the plugs am using the 300zx fuel filter have the whalbro 255. my wideband is reading right, i just dont know what it is, im pretty sure it not a boost leak because when i first start driving it, it is boosting great 11lbs. what i m leaning more toward is that my waste gate may be going....i just hope it is something a little more simple than that. i really need some help its pissing me off