I had the same exact symptoms in my 12v 57. Turned out to be four things in combination;
The coil was/went bad. Ate the condenser (or vice versa while I was learning what the resistor was for). And my engine was well out of timing, down to a bad distributor clamp. At the same time, I had black smoke and wet plugs from running too rich because it would only run with half or better choke. Replaced the Rochester B because it tried to burn my truck down on a rural road.
The coil/condenser swap is what made the difference. Second time changing both at Advance Auto, by the way. Then I was able to tell that the carb (that I rebuilt twice) was unserviceable. AMAZING difference with the new (rebuilt) Carter YF.
I don't know that it's ever as simple as just one thing with these trucks. But I spent a lot of time chasing gremlins over it...
Best of luck,
Jim
