Engine Stutter??????

[sweetr33]

Well i just baught my car on tuesday ad its got a greddy boost controller among other things. It reads about 6 or 7 on the "FACTORY" boost gauge. Anyone know what pound i would be running>? It definately aint running 6 or 7 coz it goes very well. Especially on cold nights. Sometimes i get a stutter at round 4 thousand revs in 4th n 5th but if i max out 3rd n then go into 4th in aint stutter at all. I tried turning the boost down, changing the plugs(iridium), fuel fitler and oil n oil filter and then resetting the ecu but the hesitation is still there. Since i put the iridium plugs in i definately noticed the difference in every day running, its smoother in its power delivery now and doesnt crackle from the exhaust under full load. But the hesitation only seems to happen every now n then. Could this come down to a silly thing like poor fuel?? I doubt it coz the only fuel i run in it is bp ultimate. My pod is dirty as hell even after blowing it out with an air blower but i am thinking it wouldnt be coz of that. It has stock turbo, stock intercooler if those stats are needed. Any help would be much appreciated