1989 Chevy Celebrity Engine stalls

My question involves my 1989 2.5 liter, four cyl. Cheverolet Celebrity S?W. It has 164,000 miles. Problem: It runs good and smooth for five or ten miles then the engine stops. It starts right up with no hesitation and may run a few miles and stop again or more likely it will stop right away. It is as if the engine must warm up before it stalls. I have had it at an independent repair shop off and on for about five months at a cost of about $1000. The mechanic has replaced the fuel pump and strainer, fuel filter, crank sensor, ignition module, throttle position sensor, TBI base gasket, intake gasket, fuel injector, spark plugs and spark plug wires, the battery and has decarboned the engine using a three part kit. He has tried a new engine computer with the origional card and has put in a used computer with its own card from another engine(same). He has tested with his diagnostic tool while satic(not moving) and while driving it several times. None of this has helped the problem. He tried and tried but finally gave up. I then discussed the problem with a mechanic at at Cheverolet dealership and he was not interested and said it sounded like the car is a "basket case". Do you have any possible cause for this problem? It is such a nice driving car and gets about 36 mpg on the road. I hate to part with it but may have to. Please give me your thoughts. Thank you.