I don't know diddley about turbo setups, but if the engine runs fine, doesn't make any boost, and then makes a whoosh at around 3000 rpm.... I'd guess there is something opening up to create a BIG boost leak.
Drawing on my minimal knowledge of wastegates, I think that they are controlled with some kind of 3-way valve that the ECU uses to limit boost pressure by opening and closing the wastegate. Apparently the wastegate may have a spring with a low pressure rating that works as a kind of backup if the 3-way valve/servo controller craps out. This is based on reading "... the turbo was only operating at wastegate spring pressure".
These things appear to be sensitive to having the correct ports on the valve connected to the ports on the wastegate, so it would be worth checking if that noise you hear at 3000 rpm is not the wastegate opening prematurely. Depends a lot on what kind of electronic control you have on the wastegate, and there seem to be a lot of variations, but logic says the wastegate opening is one reason why you have no boost.
If you don't have a one way valve in the brake booster line, you will no (very little) brakes when the engine is not running.
Cheers... jondee86
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