Slant 6 Turbo 68Dart Project

Maybe your waste gate diaphragm is only rated at 8psi, have you tried a Manuel boost controller to up the boost, or what you can do since a Manuel controller is basically a air bleed get a straight plastis hose connector and start with a small hole drill it on on side and see if that does anything, put it between the wastegates and turbo housing. Used to do this on our srt4 neons.