How much boost can you get to before it starts dropping off?
I had an issue with my fuel pressure dropping off after 5 lbs of boost. Turns out the pump I had was a Walbro that was notorious for failing. Do a search on "F2000169" and you'll see.
Once I installed a new Walbro GS340M from Turbo tweak and swapped out the fuel filter, the fuel pressure during boost returned.