The T3 turbo has mad lag, youre not going to get much power until youre almost at your fuel cut-off, sadly. It should be making more than 8psi, however. The first thing I would do is unplug the waste gate entirely. Just pull the hose off the waste gate side (not the turbo housing side) and clamp it or put a screw into it, just secure it for the time being. See if you get anything to change.
While you're pulling off that line check the action on the waste gate. I dont know how much movement you should get but if you feel like its binding or not getting to a fully closed position then you have your answer.
After that I would take out that huge fucking intercooler. There was no intercooler designed in this system, you dont need it to run properly. Find the stock turbo to intake elbow and run that (assuming this is a stock T3 or K24 in stock location up high on the head).
if those fail then you may have a fueling issue. These turbos are "fuel controlled" in that, you wont see much boost without the injector pump giving you a boot full of fuel. well as much as that stock pump will give, anyway.
Stock youre looking at 70hp and MAYBE 80ftlbs, not a whole lot going on there in the power department even if you're running perfectly. Where are you located?