95' S-10 4.3 CPI "W" spitting and sputtering under

Hello, I hope you can help I'm at a loss. My 95' S10 has 185,574 miles on a 4.3 CPI W motor. It recently developed a spitting and sputtering when ever you try to accelerate and if you run it long enough it will try to shut down. It has shut down on me twice. The problem doesn't matter if you are just revving it up in park or if driving. First thought was bad gas but changed fuel filter, and cleaned injectors but no change. Then, replaced distributor cap, rotor, spark plugs and wires. Still no change. Took it to a shop and they checked some of the more obvious things like injectors again and finally decided the computer needed replaced. We did that and still no better. They can hook up an external fuel source and it runs fine. I noticed that right after they cleaned the injectors it ran better for about 5 mins. I am really at a loss and it seems the shop I usually deal with is as well. I do know it has an exhaust leak and the catalytic converter is the original, could that have anything to do with it? Any advise would be greatly appreciated.