Dave when you say It overheats on hills does the radiator coolant boil and overflow? or just your gauge climbing towards the red? Is the fluid leaking out of the fan clutch? Can you spin the blade more than one rev when cold? Some times dirt can build up on the coil spring in front and can act as an insulation delaying the fan clutch from coming on. This can be cleaned off with a tooth brush and some carb cleaner. Also is you temp gauge reading accurate. You can compare the sensor reading to the thermostat reading with an IR gun to verify the accuracy of the reading. I would check these thing first before I changed it.
