94 Jeep GC Loss of Fuel Pressure Hard Start

I have a 94 Jeep Grand Cherokee with 6 cyl. that is hard to start because of loss of fuel pressure after fuel pump pre-start and after motor is turned off. When the rig starts it runs great and fuel pressure is normal 32 psi. I am in a state of denial that it may be leaky fuel injectors! I have replaced the pressure regulator but the problem persists. I noticed something odd. When the vacuum to the regulator is disconnected, the pressure is at spec at 41 psi, but there is fuel running out of the return line and back to the tank. Is this normal? It seems that would make the pressure go to zero when motor is turned off. Do I have a breach in the fuel rail that is bypassing the regulator? Can I temporarily plug the return line to do an injector leak-down test or will the pump pressure be high enough to blow up the injectors or other components?