1992 Chevy S-10 stalls out

Engine Performance problem
1992 Chevy S-10 6 cyl Two Wheel Drive Automatic

My S10 stalls out after driving awhile. I have replaced fuel pump, computer, oxygen sensor, throttle position sensor and spark plugs, cap and wires. I even took it to a garage and they found nothing, drove it around town but it never stalled out for them. To get it to stall out you have to drive it over fifty miles an hour for at least twenty minutes. After stalling if you wait for fifteen minutes it will start up fine, drive great until it warms up then stalls again. I am always by myself when this happens but the other day my wife was with me when this happened. With the air cleaner removed looking down into carb, the engine started up okay but then the jets shooting the gas stopped and it began to stall again, they would shoot gas then stop again. Now I at least have a clue what is going on. My question is what is causing this? It seems that it is a heat issue messing up the fuel delivery system.