My car had been in and out of the shop for about 6 months, while the cracked cylinder head was being replaced, after I got it out of the shop, the acceleration seemed sluggish. I bought a prseeure/vaccuum tester gauge. Test the boostpressure from the turbo. On the intake manifold (oval aluminum tube that warps over the engine) is a small hole that is plugged with a hex head metal plug, remove it and install the pressure gauge, the boost should be about 10 psi, when the engine running at about 4000 rpm, you will need someone to push the throttle while you read the gauge, the boost on my car was good, so the other problem that can cause this is lack of fuel, another hose coming off the intake manifold leads to a valve that feeds more fuel to the engine as it senses the turbo boost, i removed the metal fitting that the hose sttaches to, and it was clogged with black sludge (exhaust particulate matter), I cleaned it out, replaced it, and the engine ran like new again 
Hope this helps other people out.
Will
Hope this helps other people out.Will
