Having an awful problem and since I've had good luck chatting about problems on this forum I thought I'd throw it out for everyone else to chew on while I putter away at trying to pin it down.

I'm experiencing symptoms similar to this :
http://www.brickboard.com/FAQ/700-900/EngineTurbo.htm#TurboLosesPerformanceatBoost
"In my 760 with turbo and intercooler, when trying to accelerate quickly or when  driving up a large hill I lose performance the more gas I give it and it blows black smoke out the back. The turbo needle is about at 11:00 when this starts  and never seems to get past 12:00. I have not been able to get more that 4000 RPM's out of this car at all except maybe in park. "

except I don't have any smoke.

The wastegate and actuator both seem to be in good shape, there are no apparent air/vaccuum leaks...

When you floor it, the turbo spins like crazy as soon as you get to the point where it SHOULD be boosting...

I'm lost - I just don't know what else to do - it has lots of fuel(though I haven't tested the pressure regulator), and fire (even swaped coils), and the AMM seems to be functioning as well (also swapped this)

This all came on very suddenly - I drove it all day yesterday (about 50 Kms, mostly highway driving) and got up this morning to take it on a long drive - it was acting up as soon as I started it, and I can't seem to get anywhere with this problem.

Please help me out with any words of wisdom...