Had Motoscope on the phone today, been out in the car and it didn't fault once, ran it on the rollers later with a fuel pressure gauge connected, after a few runs the fuel pressure dropped from 70 psi to 40 psi when on full boost (5k rpm), AFR went well lean also, which either points to the pump (which is new) or possibly the regulator.

Pump still sounds like it's cavitating tho, so may have a blockage in the tank somewhere.