It might also be a clogged vent on the tank. I've had that happen on a few cars. Sometimes, if a vent is glogged, the engine will run until a vacuum builds up in the tank. If it dies after running a while (but not long enough to heat up ignition parts), that could be the problem. Easy enough to check, After it dies, immediaely take the gas tank cap off and try to restart the engine.

1977 CJ-7, fiberglass body, AMC 360 w/ headers, DUI ignition, Edelbrock intake and Holley 4150 carb, TF999, Dana 300, 4.56 gears lockers, York air comp, 4" susp lift, 2" body lift, BFG 35" M-T tires, Megashifter, AGR pump & box, REP8000 winch.