I had this on a Passat 2.5 TDI V6.
Felt like turbo wasn't working, wouldn't rev beyond 3000rpm.
Put it on vag-com and maf readings and turbo boost were half what they should be.
Basically the VNT mechanism on the turbo wasn't moving. The cure was to remove the air tubes going to the VNT and blow them out (Especially any plastic pipes joining rubber pipes together).
Worked perfectly after that.
Apparantly a 2p plastic connector gets gunked up, stops the small vacuum air flow and is diagnosed as a faulty turbo. So £1000+ later and you have the same problem.
Try the above, simple to do and check afterwards.