I would firstly look at the ignition side of things to rule this out, if you are getting spark out under boost, it won't develope boost as not enough fuel is being burnt to spin turbine fast enough, but it will just feel flat, so decent plugs gapped at 0.6mm, I would suggest AGPR12PP8 on stage 1, next check the fuel pressure, should be 3 bar with vac on, and rise to around 3.6 with vac off and plugged.
The dump valve if leaking can be tested by using a bit of wood dowel/broom handle cut down in place of dv temporarily to see if this is leaking.
I would do the cheap free things first, it's likely to be something very basic.
tabetha