1984 240 having stall issue in reverse

[taylor98v70xcharris]

Im having an intermittent issue with the car dying when i put it into reverse after i start it and let it warm up. Once it fired up right after and acted like nothing had happened the other times it would just need time and then maybe an hour later it started, making me think it was a stuck relay. Sense the first time this happened i have changed the fuel filter, both pump relays, pos battery terminal, and vac lines to the pressure regulator but it just did it to me again. Could it be the idle control valve or should i just go ahead and order a new pump? Im just about out of ideas.
Thank you.