Did you install the check valve backwards?
Did adding the check valve double the back pressure while running, as IIRC 39 is the top OEM fuel pressure for 1995???? It is 39 psi if it has a return fuel line.
The added check valve may raised the pressure enough to damage a hose seal, or damage the fuel pump CV or the FPR-check valve since you saw it reach at least 49 psi!!!!
You need to start from scratch looking for leaks from the pump to the injectors to the FPR itself. You pull the rail from the intake, make sure the injector clips are still holding the injectors to the fuel rail, then cycle the switch to see if any fuel at all leaves the end of the injectors.
Are you sure you got that fuel hose at the pump sealed 100%????
Now, one time, "if it ain't broke don't fix it!!!!"
Does it start right up all the time now????
Does it have proper fuel pressure when running???
Pretty sure mine bleeds down to 20 psi quickly with the engine turned off, and goes to zero over night, if not sooner. It runs and starts fine!!!
Lastly, is there a filter in the line!!!!! ???
You could have trash in the fuel line that is coming loose and sticking in the new FPR-check valve, or injectors, or from drain backwards into the fuel pump from decaying hose in the fuel lines!!!!
Did you just confirm the fuel pump check valve is holding pressure? You can dead end the pump to a pressure gauge, and cycle it on for barley 1 second (do not run it too long, as it might damage the pump, over pressure it??) and see if it holds pressure.