Will not stay running

I bought this for son as a first car and it drove fine for the thirty or so mile trip home. Parked it for a couple days until he could his tags for it. Went to drive it about fifteen miles to get something to eat and it started to spit and sputter every time he slowed for a stoplight. Giving it gas while stopped helped until it shut off completely and would not restart. Took it to my local mechanic and had the throttle position sensor, distributor, ignition coil, fuel filter and fuel pump replaced. Tank was emptied and cleaned while changing the fuel pump and TBI was rebuilt and cleaned. Started right up and ran for thirty minutes, then stalled. Started up again and ran for five minutes at a time maybe four or five times until it would not restart. So they pushed it outside to get another vehicle into the bay for service. Went back to it the next day figuring they had to push it back into the shop and it fires right up and they drive it in and let it run. Fifteen minutes later stalls again, and again, and again like the day before. Put an ECM in it and thought it fixed the problem. Truck ran for two hours in the shop with no problems. So my son picked it up yesterday and drove ten miles or so to a friends house and parked it, went back out to head home and made it a couple miles before it stalled, again. Took him forty five minutes to get it re-started and took it back to his friends house and called me for a ride. I am at my wits end with this and too far into it financially at this point to walk away from it. Any suggestions?