my TT T38 runs 30 psi with no problems, if you have no air leaks, good actuator (genuine garrett i use) & the wastegate is shutting then you should start looking at your boost pipes, the airbox to turbo intake pipe can suck itself flat, i got Paul Roose to do me a 5 ply intake pipe for mine, the other silicone pipe was not up to the job.
for a quick try you could remove the pipe, run the car up the road & see if its any better.