There was a recent thread where the diesel wouldn't put out full power because of a vacuum problem (I guess used to control boost). Could be as simple as that.

I'm guessing you have not driven a similar car to know if the acceleration is on par. The D has a shitload of torque and has a very snappy launch. If you aren't seeing that, something is amiss

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E53 / M54 2001 3.0i gas LHD (pair of them: his & her)