I have a 1995 Chevy Blazer 4.3 V6 with the "W" series Vortec. I am having issues with rough idle at low idle. Here is what i have replaced and done so far with zero results.

New:
Distibutor Cap and Rotor
Wires
Plugs
Hall Effect Switch
Coil
Spider Injector Assembly w/Fuel Pressure Regulator
Plastic Fuel Lines from Spider to back of the intake
Air/Idle Control Valve
New rubber Intake boot with the Air Flow sensor that is housed under it.

I took a fuel pressure reading via the schrader valve and it jumped to between 50-60 pounds but immediately fell off to zero. I took off the plenum and checked for leaking fuel....none. I pulled each injector out and energized the fuel pump(engine off)...no leaks on any of them or the regulator. Where is my pressure drop off going? I can not find any leaks based on the common problems associated with a leak. Where does the pressure test come from...the supply line or the return. Could the pump be bad...or is there any check valves in the supply line before the spider that could be bad...like the filter or pump itself.
Any ideas or suggestions would be greatly appreciated. I replaced the spider injector...and it ran great for a week...then all of the sudden developed this issue.

*+*+* scratching head*+*+*+