Fuel pressure problems?

I have recently encountered two problems with my Isuzu:
1. Upon the vehicle warming up, when you cut it off, it will turn over but
will not start up. If you let it sit for about 1 to 2 hours, it will start
and run as if there was never a problem. I have replaced the fuel filter,
mass air flow sensor, air filter, oxygen sensor, distributor cap, rotor,
wires, and plugs. I performed a computer self diagnostic and detected no
problems. I placed a fuel pressure gage in line with the fuel pressure regulator and I am getting over 60 psi (vice 42 psi max) when the engine is running. Upon troubleshooting, I determined that I can duplicate the original discrepancy at any time, if I relieve fuel pressure to the gage by removing then replacing the fuel pump relay. Eureka it is the fuel pressure regulator! Right? Now the plot thickens. If I tap the fuse box in the engine compartment, the vehicle will immediately crank however, the fuel pressure will still peg out my 60 psi gage. I swapped the headlight and fuel pump relay (same part numbers) and the problem doesn’t change. I am still focused on the fuel pressure regulator as the problem. I think the abnormally high pressure that the pressure regulator is supplying to the fuel system is causing the ECM to send erroneous signals to the fuel pump relay. I will be purchasing a regulator tomorrow, any suggestions will be appreciated. I noticed some earlier posts, in other threads, in reference to the intake manifold gasket causing idling/stalling problems. Could that be my problem?
2. Upon applying brakes, I physically feel the brake pedal gradually
losing pressure and sinking to the vehicle's deck. Unless I pump the brake
pedal 2-3 times to build up pressure, the brake pedal will continue to
sink, and I will eventually lose braking power and roll forward. I have
replaced the front disc brake pads. The rear drum brake pads do not appear to be worn beyond specifications. I have generously bled all brakes. Visual inspection of all brake components has revealed no leaks. I am not losing brake fluid from the master cylinder.

2. you need a new master cylinder. I had the same thing happen before on a work truck (F250). It got the the point where I felt a pop and then I had no brakes, and hit the car ahead of me (no one was hurt, only a couple of bent metal bumpers).