Boost Tapering Off R33 Rb25det

[RicsR33]

Hi guysMy rb25det seems to lose boost after it hits it's peak then tapers offThe rb25 has a t04e which is running .8-.9 bar (11-12psi) but once it reaches that it tapers off and is down to about .5-.6(7-8psi) by redline.. I've changed the actuator, checked all hoses and clamps.. This has got me stumpedMods (even ones that wouldn't affect this)Split dump pipe, 3inc (could be 3.5) full exhaust system with a highflow catFront mount intercoolerT04eSafcCheap boost controller (tried a gfb and did the same thing)Standard manifoldPodThere's more but irrelevantI'm not to sure if a boost leak would do this?? What do you this could be causing this massive drop?