1999 Jeep Cherokee check engine light

1999 Jeep Cherokee mileage: 103,000. While on a trip check engine light came on forty miles into trip. I pulled off and checked fluids, all okay. The vehicle cooled downand all of the gauges looked okay. I continue on with the trip and in another forty miles the motor acted as if it was going to cut off. I pull off once again and let it cool down. The vehicle starts immediately and runs perfect for another forty miles and then it does same thing. I notice that I cannot set cruise control. I have replaced fuel filter, spark plugs, plug wires, distributor cap, rotor button, and ignition coil and I still have the problem. The next move is the EGR valve. I called the Jeep shop to order part and they say I don't have an EGR valve according to their books, and it must be something else? I took it to a shop and they read the codes, there was nothing out of the ordinary, all sensors are performing correctly and they cannot recreate problem. They return to me unrepaired and still can not set cruise control. What gives? EGR or oxygen sensors? I would gratefully appreciate any insight you may have on my problem. Thank you.