1991 Pick Up Ole' Betsy slow death

I am the proud owner of a 1991 Isuzu P' UP with a 2.3l gas engine. I have put 230,000 miles on this truck with no major problems. In the last few months the idling has been eratic when cold surging, fast etc. Now and then when you would start off to drive the engine would sputter and almost die. I replaced the gas filter, cleaned the needle valve screen, plugs, plug wires and distributor cap. It gained a little power and was still having idling issues but drivable. I started off to work the a couple of days ago and got about one block and the engine died when a load was put on it. It runs at idle speed but when the pedal is depressed more than half way it will kill the engine. Thank you for any advise.

Derek