First thing I would do is run a pipe directly from snale (turbo compressor housing ) to the actuator , therefore bypassing all the electronics and see if this drops boost , if it brings it down massively then you are either looking at a stuck boost solenoid or faulty wiring from ecu to solenoid valve . Would then put it back see if you can borrow a different valve then if it still overboosts , if it does then will have to disconnect ecu and check continuity from solenoid valve to ecu connector .

Hope this helps