Mechanical fuel pump.
I removed the couple of gallons of gas that had been sitting in the tank over the winter. With fresh gas, it did stumble a bit for a few minutes then seemed to run just fine (assumed any bad fuel in the line and carb was combusted in those minutes).
There is a fuel filter between the pump and carb.
I could not get it started again to drive it the block back home at that time. I came back 4 hours later (truck had been sitting in the shade) and after much trying, eventually got it running. After revving the engine for a minute or so, it idled ok, and I took it for 20 minute drive where I had a couple of stop signs and speeds up to 60 mph. It seemed fine.
The engine started right up (maybe 3 seconds on the starter) at 11 AM and 96 degrees the next morning and idled as smooth as it ever has.
