Overheating Overheats while towing up hill

if it has a viscous fan hub , replace that hub
your statement indicates that it is the hub and in addition to hills and high rpm it will also be noticeable at stop lights or slow moving traffic

if you are selecting lower gears on a stick shift... good... if the car is automatic you should leave the shifter in drive position going up hills or towing. use lower gears to go down hills only. check the cooling fans for proper operation. also... their is a product or additive you can get called "Water Wetter" add this to the coolant to help the cooling system work better. Also, the engine thermostadt may me malfunctioning.

where is it located....thermostat

first check the fluid --thats its full--smell and look at fluid if brownish and smell burnt need to change filter and fluid .check the trans lines for damage/kinks .check the cooler thats its not clogged or damaged .also check what ur towing [correct weight -not over rated for truck] that wheels or if has elect asst brakes they are nor dragging

check for engine block clogg

How about a temperature sensor? If it's faulty it could be sending the wrong messages to your computer and your dash light.

you might want to have a radiator shop run a flow test on the radiator to make sure it isn't partially plugged up. it is almost impossible to guestimate if it is plugged up partially without a flow meter. and on most computer controled engines the sensors depend on the thermostat to keep the temperature within the operating range of the sensors.

you just said it you need a new fan clutch

did you replace the thermostate, did you cook the head you reconditoned ,as they may still give you grief,some only last2000km after recond.

Did you ever sort this ? I've a similar overheating issue and just wondered ? Thanks ...