Well, I've played with the truck some more. I think it's carb problems. It does get worse as the engine heats (beyond where the temp gauge stops climbing, though).
I've got good vacuum (as tested with the hand over the intake that goes to the air cleaner). I did discover that it was running overly rich; adjusting the air screw made a good difference in the overall idle. The stalling problem persists, though.
There is a very noticeable hesitation when first applying throttle. The engine will either stall and stop or will pickup and accelerate, depending on-- I don't know what.
It's possible I have weak ignition. There is a spark booster unit sitting on the coil, but I don't know how to check it. The engine starts fine when given a squirt of starter fluid. I also seems to run without missing (during the times it is running!)
Gas coming through the jet into the carb throttle barrel seems to dribble in when the accelerator is first pulled (that hesitation period). If the engine stays lit, the gas will then spray in as the engine revs. The accelerator pump seems to be working ok.
