Pickup lags every time I try to accelerate. I replaced distributor cap/rotor, plugs, wires, fuel filter. Seems like the truck is not getting fuel, but I don't know. Hoping to not have to replace carburetor. Please help. Somebody have this happen to them?

 

Have you checked the timing? Have you checked for vacuum leaks?
If not this should be your next step.

 

Very unlikely it's the timing. This started happening over the course of a 30 minute drive. Hadn't touched anything under the hood.

 

Could be problem with your accelerator pump? I am more familiar with the 22r's though. I've found over the years that a disassembly and cleaning of the carb on these old trucks will often get them running smoothly again.

 

Could also be the filter in the gas tank if the 20R's had them. Picks up crud stirred up while driving and gradually chokes the fuel flow. Somewhat common on the first gen trucks.