Could be couple of different things so bit more info would help...
- history (when did this start, what was it like before, anything changed before problem, etc)
- full drop of power or just significantly down on power - does it run when revs drop or dead?
- mapped or not?
- any warning lights?
- tried a code reader for CELs?
- any difference if a load on the engine or just rev it up when in neutral?
- boost pressure just before cut and @ cut
couple of options that come to mind with current info:
* limp home mode
* rev limiter set @3k (if mapped like)
* bad coilpacks
* over-boosting and ecu safeties kicking in