I turboed my Toyota truck (V6). The pump on that had a shut off pressure of 50 psi. The volume was also lacking. As the revs went up under boost the pressure would drop, was running 12 psi at the time. I put a Walbro 155 l pump in . You're only at 5 psi though so I doubt that's your problem, you should check the pressure under load though. What are you using to control fuel under boost? Z32 turbo ecu?I run an aic with 2 extra injectors. Once I had the pressure switch loose a signal and I could not run over 2 psi without it falling on it's face.