Although you said you have no codes, so that kind of rules that out.
~6psi is the wastegate pressure, so it seems like your wastegates are working fine. maybe the boost solenoid is not closing? Try blowing air through it when its powered on.
------------------------------------------------------------------ 1992 300ZX NA 5 Sp (Dead) 1990 300ZX NA Auto 2+2 (Dead) 1990 300ZX TT 5 Sp (Building) 2004 G35 Sport 6MT (DD)