These trucks are very picky with fuel preasure. Key on enigine off you wanna see 60-62psi and no less than 55psi after 10 mins.
Andrew is correct some fpr 's are adjustable or could be seated poorly. Check that the nut kits is seated correctly as well.
I have a 1995 w motor and idle at about 56psi so your idle to me anyway is a bit low.
Definitely change the fuel filter, was miracles for mine.
Check for proper PCV function if not just changing it all together. And with that of course run threw and check all you vacuum lines.
Check for good spark. Your looking for brilliant blue / white spark. Yellow or orange spark won't work.
If you do end up having to do a tune up, do a complete tune and use only delco parts.
Good luck bud report back.

 

Changing the fuel filter was mentioned I know it would be a pain the rumpess but its possible the screen is clogged on the bottom of the fuel pump inside the gas tank.(Worse case)I would also suspect clogged or dirty fuel injectors.I have heard it mentioned on this forum and couple of others that these years of the 4.3 are picky and finicky about what brand of distributor cap.I found this to be the case on my 94 chevy truck also.Make sure your spark plugs are gapped correctly also seated in and not loose.Sometimes they have a tendancy to come loose even after tightening.

 

Clogged injectors wont cause low fuel pressure. Not to say its not your problem, i just havent seem evidence of it. Delco plugs always seem to be a must as well with these things. If the leak down test goes well id stray away from a fuel issue. If the regulator is ajustable it can easily be adjusted for a higher fuel pressure.

 

Heres something else you can check if you have low fuel pressure and its pretty easy.It would be rare case sceanario but I seen it happen.On top of the engine where the fuel lines going into the top of the regulator theres a clip that goes inbetween the fuel lines and holds them down in place.Theres 2 nuts that hold the clip tight,I would check and make sure they are tight and lines are seated all the way in.I have also found rust in the gas lines themselves thats why Im changing mine.

 

Today I checked fuel pressure drop with engine off, ignition on. At first it was 56 psi, then dropped to 46 after 10 min. Changed filter, then had 56 psi at idle, and 62-64 when blip the throttle, still runs terrible. Then re-tested pressure drop with key on and enging not running. same 56 psi, but now pressure dropped to 0 in a few seconds.
I changed the regulator, disc inside looks cocked. Now engine off, key on psi is 64, but drops to 44 in minutes. Still runs terrible. Pulled top of plenum again to look for leak. Pulled out all injectors, turned key on, same 64 psi then drops to 44, but no leaks. Any ideas? This thing is a pain in the butt.

 

Pulled the injectors out and cranked the engine over. Seems like no fuel comming out of #1 and #6. Been running sorta rough for somer time, now really rough. Could it be 1 injector clogged, then a second? but not sure why the leak down.

 

Dirty injectors on this one.I would try running some seafoam through your gas and then take your vacume line off the brake booster and pour in slowly till you empty the can.You will have to keep indling the engine at high revs when you do this.Gosh I just hope when I get mine runing I dont have any prolems.

 

I removed the regulator and the disc was cocked-not seating. So I replaced it, didn't help. Then I took the solinoid part off the main body of the CPI and blew air through all 6 ports and tubes. Tubes-injector poppits for cylinders 1 and 6 seem to be stuck open, no resistance at any air pressure. Replaced the CPI with a Borg Warner rebuilt unit from Pep Boys, $216. Runs good now. The old rebuilt unit was $300 a few years ago from ebay, didn't last. Now I need to see if I can return the new regulator I bought, cost $50, used for a few minutes. Thanks all for the help.