ok i looked an looked but couldnt find anyone with the same problem as i.
here it goes, i recently aquired this 83 chevy 6.2 k30 when i got it it ran fine started right up in -20f no problems, it STILL starts right up and fires right off, but i was out driving one day and took my foot off the pedal and it just died, the fuel tank was leaking also so i downed the truck for a month or so replaced the tank, the sock, the tank selector valve(it was fine except for its run in with my PLIERS) some seedy looking fuel lines, and the filter. bled it out a bit it fired right up BUT it still has the dying problem if i let up on the pedal suddenly. it idles (purrs like a kitten) no hitch no missing no UNUSUAL smoke runs great on high idle too, and i can ease the pedal out slowly it wont die. i took off the top cap of the IP and checked the check valve and smooth movement of them plungers in there. it only dies if i let out on the pedal suddenly and it does it in neutral park or any drive gear, im at a complete loss ive drawn some bad conclusions need some more suggestions before i go nuts with my pliers again thank you

Usually if the slow idle adjustment is'nt right,it'll stall on deceleration.Try turning the slow idle screw inward 1 full turn and see if that helps any.

ok thank you havent tried that yet ill do it in the morning and see how it goes

if not check the return line coming off the pump and see if it's plugged a bit. i had the same problem, not totally sure what i did to fix it but that was on my list as well.

if that fitting on the top of the IP (i call it the check vavle) is stuck open it will cause your symptom.

PO had a fitting that was just a pass through installed replacing the check when i was first bought the truck, the mech could not figure it out. He finally put the check back in and then it wouldnt die.

If that check is stuck closed it will kill the motor and wont run at all until pressure is released.....had that happen as well. It wont even start if thats the case.

if it is plugged off you need a new governer weight retaining ring... not uber hard to install or expensive. just make sure you clean as many of those particles as you can out, or it might plug up again. just make sure you get an elastomer style retainer. the other two materials get a little brittle after time and break apart.
probably wouldn't be a bad time to put in a new metering valve either... or clean that one up. turn if around in some 400-500 grit sandpaper soaked in some diesel. That could be causing the die-at-idle aswell.

both of those parts are right inside the case ontop of the pump, and not to hard to replace (well the metering valve can be a bitch if you don't take the intake off, but only when taking out the throttle linkage.)

well i had to turn the idle screw in all the way to stop the dying off problem now it lopes at idle, i took off that top cap of the IP again, rechecked the check valve its clear of debris does the tension on that spring give out? can i replace just the top part of the IP? do they even sell that? and someone was telling me them old IP's cant take the low sulpher diesel fuel it wears out the pistons cuz it doesnt lubricate and i need to add a fuel additive. is that right or just a wild rumor? governer weight retaining ring? what does that do, and more what does it look like? sigh, and if the lift pump isnt supplying properly will that lead to a drop in pressure when the engine rpm's drop and cause a um vaccum or something? ok lots of questions im sure ill have more but at least its running before i do something else major i need to get my ford up an running you never know i MIGHT have to go back to work.............

take the hose on the top of the IP off and check to see if it's clogged a bit in there. but as far as additive's go, it never hurts, and the uls diesel is a little bit dryer. if that doesn't work and you think it's the lift pump, pull the output on your secondary filter right above the engine, and hook up a hose and see how it sprays. if you think it might be the LP, it never hurts to replace it with an electric one and block off the mechanical slot. makes bleeding alot easier anyways.

The gov. weight retaining ring, or FLEX ring, as its called in the business, breaks-up over time and turns into, what looks like "coffee grounds".. If you've had the top cover off and didn't see ANYTHING that looked like that, your probably ok. Most, or about 80% of all automotive pumps were converted to a "solid weight retainer" called an E.I.D. in the early 90's.. and signified w/ a metal tag on the top cover screw, stamped "E"..

thank you guys youve all been very helpful, and i learned some stuff i didnt know before which is ALWAYS welcome. thanks again the "tank" is running much better quite well for what its been through lol