A few things:
What spring do you have in the valve? You mentioned yours not having a silicon hose with it, so I assume that you either purchased it used or purchased a generic 004 instead of the MSP specific kit. We have springs rated for more than 30 psi, if one of those is in the valve it would only open a small amount at the boost that you are running if at all. You are going to need either the BLACK or the GREEN spring in your car.
You mentioned improved throttle response and spool, this would eliminate the possibility that the valve is stuck open and make it unlikely that the valve is stuck closed.
There are two pistons in this valve, the discharge piston and the idle piston. Each have their own spring and we have varying tensions for each. At idle the discharge piston will be pulled upwards by engine vacuum overcoming its spring, the idle pison is beneath the discharge piston with a spring sandwiched between the two. This spring pushes the idle piston downwards under vacuum (or very slight positive pressure) in the boost hoses to prevent a loss of metered air at idle. When shifting, the sudden vacuum in upped portion of the valve will pull the discharge piston upwards just like when at idle, this allows the idle spring to decompress thereby lowering its tension on the idle piston, at this point the charge air is pressurized and forces the idle piston up allowing the valve to vent. If the tension on that spring is to high the valve will not vent.
Sorry for the length of this post.
If you could send me some pics that would help out.
Give us a call at 407.447.5363 and ask for Patrick, its usually easier to handle this sort of thing on the phone.