Check the wastegate on the turbo and see if its causing the turbo to drop off the pressure. The tube from the turbo to the wastegate could be leaking and causing the pressure to be lost. If you need further...
Hi there. The wastegate actuator is not functioning correctly or the boost sensor (https://www.yourmechanic.com/services/barometric-sensor-replacement) is not working making the turbo boost properly. Check the wastegate actuator hose (https://www.yourmechanic.com/services/wastegate-hose-replacement) and see if its broken and listen for leaks when you drive...
