guys i brought a piper cam kit before for my old rst turbo with ...
ahmed stage2 chip
-31 standard turbo bleed valve
piper 285t kit
radtech front mount
exhaust and good filter ect

and anything above 14psi and i would get valve bounce with brand new piper springs fitted so i put double valve springs in and afterwards it was peaking 19psi and holding around 16psi and made 192bhp ...

and another one i had that had a problem like this was a sticking wastegate and ive brought faulty actuators so could be anything