Turbo spooling waaaaaay high!, need boost to come down......how?????? Options

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Hello doctors, get your surgical gloves on, because i need help.....
i have asked this question before with no solutions, so i will try again, maybe someone will pick up something i missed, hopefully!!!!!
basically, my 94 celica gt, which i swapped a st205 into, was up and running last may ( 2011 ), ever since then, my boost climbs to around 19-20psi, i have hit fuel cut twice, and smacked my face into the windshield the first time ( seatbelt safety ),
anyways, in order to stop hitting fuel cut, i have to let off around 5500-5700rpms, because im right on 18psi, and dont want to keep hitting fuel cut....cant be good
so heres what ive trouble shooted so far:
hooked air compressor up to wastegate with 15psi pressure....opened perfectly, quickly and smoothly
have an XS Power DP, checked to make sure the actuator clears the DP flange....it does
there is a line that comes off the wastegate and goes behind the bottom of the intake manifold to a sensor called a VSV valve???? i think its called, anyways, hoses are hooked to that and return up front, cant remember where the line goes up front though??
thats about it, kinda outta ideas

I was thinking of purchasing a manuel boost controller, but isnt that for turning up boost, or can you turn down boost as well ( explain please )
If that doesnt work....is there some sort of a bleeder type valve i can buy, to vent some pressure, or does that screw-up vaccum

Thanx, hope one or alot of you have an answer to my problem 6GC

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cool guys, went down the street, actually, went down a backroad highway, and i couldnt really open it up to much, only because of the no insurance thing, the fine is $560.00 for not having insurance, and they tow your ride as well, not to mention, if i went by a cop, definetly would be an excessive as well, but i did take it all the way up in second, was around 6200rpm and @ 16psi, didnt want to push much more, only because the rpms were rocketing very quickly...inbetween looking at boost rateing and rpm guage, i didnt want to blow a shift! so, i tried this 4 times on a stretch of road, and my #s were consistent, so far looking good!! no hesitation, or exhaust popping! very smooth and powerful! i know im right on that fine line though, when i reached about 4800rpm i was at 16psi, it just passed 16 but not quite 17 @ 6200rpm, this tells me, it seems to be holding now.....where as before, i would be at 18psi @ 5500rpm and going higher, would have to let off so i didnt hit fuel cut. the exhaust sounds awesome @ 6200rpm with that silencer in there...very deep, angry tone! it feels like i gained power by adding some restriction... it was never this smooth before, i like it!!!
just curious fellas, what is 16-17psi in bar form, everyone rates they'r boost in bar form.....this is something i never took the time to understand, please enlighten me, ( sorry if this is a stupid Q. ) i honestly don know, thanx-a-lot!
will have to test it in third gear on a load next time.....hope all is cured, all this from adding a simple silencer, craziness