Wastegate Issues

[sleepydsm]

1992 Tsi AWD 5 spd blah blah blah

I have an external HKS standard (40mm) wastgate on my exhaust manifold. It has a "1 bar" spring (its yellow).
Mods:
BR 20G
FMIC
660 Injectors
SAFC(five knob)
GM Maf/Maft
Greddy Type RS BOV
255 Fuel Pump
Adjustable FPR
CAI


My Setup:
I put a manual boost controller on my car today, preping for the RF rice day tomorrow. I put the MBC on a line going directly to my wastgate. That vaccum line starts at the intake manifold, goes to a t, and then to the wastegate. My bov is hooked off the T fitting.

The Problem:
At WOT, maybe 85%+ throttle at least, when the boost goes past 20 the car studders and shakes. Its as if the wastgate is fluttering, kinda like howa a BOV does. This only happens when there is a boost controller on the car, and its above 20 PSI. Anyone have any ideas whats wrong? I assume my wastegate is fine because it works as it should when the MBC is NOT hooked up. Thanks!

Kevin