Your key on prime pressure is low but your running pressure is fine. Tape gage to windshield and take it for a drive. See what gage reads when your under a high load condition.

Test regulator while engine is running by attaching vacuum hose and seeing if pressure changes. Going up is ok but falling is not.

If your losing pressure it could be because of leaking injectors, clogged fuel filter or, pump connection in tank can be leaking. This is in addition to a regulator that leaks back.

Did you smell gas when you took vacuum line off regulator. That's a sure sign of it going bad.

Since your pressure was 42 psi at idle with regulator out of the loop, pump is good at idle. I want you to test it to see if pressure stays good, with reg out of loop, under high load driving.

Also drive it with gage attached for a long enough time to see if pressure falls as pump works for that time period. A worn out pump can have pressure fall during a long drive.

 

Great thanks, ill run threw the steps and keep you posted. Thanks!