1982 Other Chevrolet Models I cant figure this one out?

Engine Performance problem
1982 Other Chevrolet Models V8 Two Wheel Drive Automatic unknow miles

My truck cranks fine, idles fine, but when driving spits sputters and dies. It has all the signs of bad gas, but its not. Ive changed the fuel filters drained the gas and even ran "HEAT" and "seafoam" thru it. Ive changed the plugs, wires, rotor, coil, and cap. Ive even put an electric fuel pump on and bypassed the mech one. The kicker being, it doesnt do this all the time. It may run fine for a trip of 60 miles, and the next time I drive, I may not make an 1/8 mile from the house. I dont know much about carburaters, but what else could it be, and wouldnt the carb act up all the time?