accelerating Jerky acceleration

[CHill3103]

I have a 2007 impreza 2.5 wrx. I've been having an issue with jerky acceleration/ no acceleration at the 4000 revs mark. Steady acceleration past 4000 revs doesn't jerk but when I put my foot down it jerks like crazy and sometimes doesn't accelerate. I have cleaned throttle body/changed maf sensor/replaced fuel pump/changed air filter and no joy. Any help would be much appreciated. Cheers 

 

[Tidgy]

Sounds like its hitting boost/fuel cut. is it decatted and mapped for it?

 

best bet get it on a dyno and see whats what, could be as simple as a boost leak somewhere.