[rayne3rr0r]

I have a 1988 chevy k1500 4x4 and whenever I fill up with gas it starts missing real bad and idle surging and dying at red lights it has a new fuel filter and fuel pump,ICM,distubitor and cap, but when ever I get down below half a tank it starts to run just fine like nothing was wrong

[TxGreaseMonkey]

Thoughts:

It sounds like it may be a bad ICM, even though it has been replaced. Have AutoZone test it for you. I don't know why the fuel tank level is affecting performance. Have you replaced spark plugs in the last 3 years (ACDelco only)? How about the coil? Ignition components may be getting heat soaked, when you stop and fill up with gas.

I would also check for codes, test all under dash and under hood fuses with a test light or multimeter, clean the main ECM ground, and ensure the fuel pump relay is fine.

[rayne3rr0r]

I don't think this truck has had the spark plugs change in the last 3 years and will auto zone check my codes too but also my light comes on and then goes away it never comes on and stays on

[TxGreaseMonkey]

Because your truck is OBD I, AutoZone won't be able to check for codes. Consult a Haynes Manual for what you need to do. It's always one of the first things you want to do. There may be "soft" codes that have not yet caused the CEL to stay on. These codes may provide tips, however, where the problem resides.

[CaptainRich]

Did you take a good look inside the fuel tank when you had the pump unit out? Reach in and try moving the tank baffles?
Hmm... I've seen those baffles break free and move around.
The one I remember most was on my truck, a new truck still under warranty: the truck would run out of gas even though the needle showed over 3/4 tank remaining.
The baffle would move while driving and stop under the fuel float, tricking me into thinking there was still fuel when I was slowly running out. You could have something choking off the pump intake.
Rare? Yes. No doubt.
Possible? Very much possible.
With everything you've done...

[biff26]

Possible purge valve malfunctioning (stuck open causing fuel to be drawn through plastic evaporative line into the throttle body) remove hose when symptoms occur and see if vehicle running performance returns to normal (be careful about spilling gas on hot engine or ignition components)