I would put my money on an Airflow meter/ air leak problem.

Start with cleaning the element with alcohol because they can get gunked up. You may be hitting the boost cut with a confused computer.

Check again that there are no air leaks from the back of the airflow meter to the inlet manifold. Also check you have all the fitting plugged up on the inlet manifold because there are a hole heap of them that you don't use.

this is very common on hotwire a/f meters, i would have cleaned this first as well

sounds more like blocked exhaust mate, had that with a fair few turbo motors

Why would it be a blocked exhaust? He doesn't have a cat and the thing dies, it's not just down on power.

the guys at the shop are very buzy but the out come atm they think not confermed if afm or fule pump, should know on monday