Re: 1998 Jeep Grand Cherokee 5.9L
When you are on the highway, the electric fan should not be necessary for the cooling, the forward speed should be enough.
Besides that maybe the cooling fan is not working, there seems to be other cooling problems as well. Was the thermostat changed lately? Is the radiator not plugged?
Is there no junk yard in your nabourhood where you can find the temperature switches?