Sounds like it could be misfiring. Does the CEL flash?
If it is that, then the cure would be new coil packs and plugs.
Similar thing happened to me, this is what was wrong. Im never was able to pinpoint it, but it is almost back to normal now. Just waiting for my coilpack spacers for my TSI coils.
Vacuum line going from boost guage splice to fuel rail was split
Coilpacks/plugs were bad
Upper Y pcv hose was cracked and leaking badly (causing most of the loss in boost)