Do all the following:

1) Check the performance of the wastegate as indicated in the other post.
2) Disconnect and reconnect the AMM harness from the AMM.
3) Disconnect and reconnect the knock sensor harness from the ks.
4) Check to make sure that the CBV (if this is a garrett) is tight and isn't leaking.
5) Run a cycle or two of STP Fuel System Cleaner through
6) Make sure you are running 91 or greater octane. I actually favor 93, and think anyone that runs anything under 91 is making a mistake. Turbos are high performance vehicles, and higher octanes provide better performance, ESPECIALLY under boost (since a turbo demands higher octane to burn evenly under higher compression). Anyway, under full boost a lower octane will burn unevenly, pre-detonation, etc., so why risk it for $2 a tank.

There's some other stuff you might do, but this (along with the earlier stuff) would be the core items I would check.

good luck,
rt