Could be a couple things, potential boost leak somewhere... pull the cold air off and get a silicone boost leak tester and put air through the pipes and see if air leaks out anywhere. and i found this out the hard way, but there's a little hole on the bottom that suppose to be there.
another common thing is the waste gate is internal on the 19t i believe. it could be out of place or loose and it may not be completely covering the hole and not building until high RPM and making little boost.