I have a 1987 jeep Cherokee Pioneer, we have replaced the radiator, thermostat, and water pump, cannot solve the overheating issue we are having. Not leaking any coolant. We have the heater cranked on high, and we can go approx. 5-10 miles and then we are in the red.

 

Can you verify the temperature at the thermostat housing? Your gauge might be reading wrong. A cheap IR thermometer will work to verify.