I'm ready to sell this ship anchor !

[lmk]

My 90gt was running great, then a month ago it dies in traffic. At home I can sometimes get it started but I have to rev it to 3000
to keep it going, as soon as I take my foot of the gas it abruptly dies. When I turn the key to the on position it will prime the fuel pump then a few seconds later it primes it again and again and again.But my fuel pressure is holding at 40 psi. What would cause
it to continually prime the pump without turning the key off and back on again? ...So far these are the parts I've changed

Coil
stator in distributor
ignition module
wires
plugs
computer
eec relay
fuel pump relay
ignition switch
fuel pressure regulator
fuel filter

The only code I get is a 15

I don't know where to go from here any ideas.....lmk