92 Chevy 4.3?

If it always starts and runs good at first when the engine is cold, it sounds like you have a closed-loop-only problem. Check the wiring and connectors to all your sensors and actuators. Unplug and re-connect all such connectors, checking for signs of corrosion while you have them off. Also check the vacuum hose to the MAP sensor.

You didn't mention what model Chevy, so go here, and select your year, make, model, and engine. Then click "Driveability & Emissions", then "Electronic Engine Controls" and go through the links in the box on the right.

http://www.autozone.com/shopping/repairGuide.htm

P.S. Don't bother looking for a "Cold Start Sensor. They only use those on mechanical fuel injection systems. There is a "Coolant Temp Sensor". Unless you're in England or Australia or something, and even then....

Also, if you start leaving things unplugged while the engine is running, it will set a lot of trouble codes, and just make it harder for even a qualified mechanic to figure it out.

Although that might work in a pinch, because with the coolant sensor unplugged, your car will never go into closed loop. (the computer won't be active)

Not the same engine, but a few years ago, I had a Ford that did exactly the same thing and it was the cold start sensor. The car would die, wouldn't start. I unplugged the sensor and it all worked. If you unplug and it works, you know where the fault is.

that truck has two filters one at the carb and one under the truck it is a big can like filter i think that is your prob. its just not getting an nu ff gas.