Cummins isx 2350 boost problems

[Lunchtime92]

Hey guys, I have a 2014 kenworth T800 with a cummins isx 2350. I put a brand new turbo on it a few weeks ago and noticed eversince that over 1500rpms I can't maintain boost pressure. It will still build 25-28psi of boost, but won't hold it. It will constantly fall back to 15-18 psi then build back to 25-28 then immediately fall back. It does this nonstop over 1500rpm. It hold 30-32 psi just fine under 1500rpm. Also the only fault codes im getting are spn 651, 652, 653, 654, 655 fmi 7. There is no audible skipping or misfire, so I changed the injector wiring harness. Faults still comeback within 20 miles of driving. Any help would be appreciated.