I had this problem with my 32 gtst, while driving it would cut in and out of boost, turn it self off. Had 3 different mechanics and auto elecs on it and still couldn't solve it. changed ecu, all sensors, fuel pump.
Then i took it for a drive with michael at turbo tune and he fiddled around with the tps sensor and it ended up being a faulty tps. We got one from jap land took ages put fixed the problem. I'd give that a go.