Truck stalls in reverse when hot

i have a 1990 chevy K2500 5.7 350 tbi with 255000 miles on the body and engine. transmission replaced at 200000. when i drive long enough for the truck to get hot (ie. 10 minutes or so) if i put it in reverse to back into a parking space or my driveway, it just shuts off. i have had fuel filter and fuel pump replaced but what could cause this? it will stay on if i dont drive long enough to get hot. i just dont understand what would/could make it do this. any ideas?

Drive it to get it hot, then, while idling, wiggle every wire you can reach under the hood.

Can you give it a little throttle in reverse and keep it going?