Bart: I had a very similar issue with my truck. 55 235 with stock intake and carb. Fortunately I have a Glass filter in the fuel line on the line from the tank to the pump. Sediment would slosh up and cover the line to the pump opening. When I came to a complete stop it would settle back and I was fine. Now I just clean the filter regularly and all is fine. I have another in the line to the carb and it is still clean so the first one is doing it's job. My fuel pump is happy as well. If the float is set too low I run out lean at high RPMs. So I don't think that is the issue. You might see that the wires to the coil cannot move into something that will short them under strong deceleration. Let us know what you find.
