[rawill]

I would certainly check all vac hoses first.
Then, if you haven't checked and cleaned it, check the APC valve, both electrically,ohms reading, and clean it out with carb cleaner,brake cleaner or similar.

They get gummed up.

Then if no improvment check the it gets max boost by disconnecting one of the hoses to the wastegate so it stays shut.

But note: you can get to "fuel cut" easy.
Not a good thing to overdo.

But it will tell you if the turbo is working fine.

 

[rawill]

Do you realise that you have modify your ECU, both a small hardware tweak, and a change to.the software map if you change from T5 to a T7 valve?