96 K1500 4.3Vortec Won't stay running

96 K1500 Vortec 4.3L, 76K miles.

Truck will start and stay running for 5-10 seconds. FUle pressure rails 60PSI gaige hooked up on downstream side of fuel filter at key-on. Fuel pressure slowly drops as engine runs, engine stalls at about 40-45 PSI.

If I key-on and don't try to start engine, fuel pressure initially pegs gauge at 60PSI, pressure slowly drops off at ~5PSI/Sec after that (I think - can't remember this part very well)

How do I determine if this is a fuel pump or fuel pressure regulator? Any other suggestions of what could be wrong?

mine started doing that over about the course of 20 minutes or so and faster under "load", i had to replace the pump. but you luck out as yuo can just buy a rebuild kit, i have a 00 and i had to buy the whole unit ($650). i suppose you could start with checking the resistance through the pump when it's on. i'd just check it from the plug itself as the pump shouldn't run out of the gas. the tank drops out real easy, then you could just stick some wire on each pin and put the connector back together, making real sure you don't have either of the two wires touching each other. then just hook your ohm meter up to each wire (making an adapter of sorts)... i'm not sure what it should be but someone here can tell you i bet.

hope his helps
lee

Replacinng the fuel pump fixed the problem. I dropped the tank, but couldn't get the steel line fittings on top of fuel pump loose (rounded them off even after sprayinng with penetrating oil, using proper size line wrenches, etc). Had to remove bed to get better access to fittings. Job was a royal pain, but one $80 Autozone fuel pump later truck runs great. I've had a bit of a rough idle for the two years I've owned the truck, it now idles butters smooth (perhaps had low pressure since I bought it?).