Ok looked for other threads on this but couldn't find any.
so my 2000 jetta tdi is over boosting. car has egr delete Malone stage 1, pp520 nozzles and exhaust and intake. my boost gauge hits about 26 or 27 than will slowly drop as the rpm rises and will hold at about 15 around 4000 rpm. doesn't matter what gear does the same thing. wondering if its waste gate control issue but im not sure.

 

Overboost will show an error code.

P0234 Boost Pressure Regulation - Limit Exceeded (Overboost Condition)
P02CA Turbocharger/Supercharger 'B' - Overboost Condition
03201 Adaptation Overboost - No or Incorrect Basic Setting/Adaptation

What error codes are you getting?