I responded to your other post on this issue in the 5.0 section, I didn't see this post till now, but I copied what I wrote about it here.
" If your fuel pressure is still low then I suggest possibly a new fuel filter , or a new pump. You should be getting 35-40 psi at idle with the vacuum hose connected. I suspect its starving for fuel until you drop the hammer , then the vacuum drops off and closes the fpr. "
90 LX Hatch, 5.0 bored .030 over/e303 cam/Ford Racing upper/lower polished cobra intake/ford racing polished 70mm throttle body/30lb injectors/ adjustable fpr/ 255 walboro pump/Ford racing aluminum x302 heads 1.7 roller rockers/bbk shorty headers with bbk catless xpipe/ 3.55 gears/tremec Z spec t5/ 5 lug conversion/Cobra front breaks/sub frame connectors/bbk upper/lower control arms