CIS stall mystery

My 1981 truck has been stalling when the engine reaches temp recently. When I try to start it again, the fuel pump doesn't kick in. If I wait 15 or 20 minutes, it will usually start again, but only until the engine reaches temp again. I'm thinking the coil, the warm pressure regulator, or? I tried a different ignition switch, and different fuel pump relays. By jumping the relay socket, I have gotten home a couple of times and the truck seems to run fine that way. I don't suspect the fuel pump itself, but who knows? It seems like when something other than the pump (I could be wrong) is failing when the engine warms up. Anyone got a clue?