Your problem is not the wastegates. The stock wastegates also have an automatic holding pressure of 5psi. Haven't read your previous post, but I believe you're ECU is putting the car in safety boost mode which wont let the car boost above 4-6psi. I currently have the same problem, but I believe my ECU or wiring harness has gone bad because I have done everything possible to fix it. Let me know if you figure anything out.