I have had a similar problem, my 33 GTST was cutting out spitting and coughing when under load (even felt like boost leak and wasnt getting as much psi), my AFM was ok, I replaced fuel pump and still had the problem, had a pressure test done and there was a hairline crack in a hose, the hose that goes to IAC valve (Idle Air Control) and it runs like a dream! sounds like a similar situation JackVGX3.0 im not saying this hose is your problem but might pay to check it out!!