Hello and good afternoon. I read your previous question and am sorry for the delay in getting a response. You may have a fuel related issue and since it happens after an extended period of time, it's difficult to hook a fuel pressure gauge to the car. Try this and see how the car behaves. Pick up a blue propane bottle, like you would use to sweat pipes. The small normal one that they sell in hardware stores. Hook a vacuum hose to the end of it and T it into a vacuum port going into the intake manifold. When the car starts to stumble, open the valve on the bottle allowing propane to flow into the engine. If the car regains some power, it would prove that fuel is at the core of our problem. Our next task would be to determine if it is the fuel pump, or control over the fuel injectors that is our issue. Start with this test and let me know what happens.
Your JA Expert,