Over heating we have put in new thermostat new clutch fan water pump going up hills gets hot going down hill cool down

If the check engine light is not on, it could be a restriction in the exhaust or mechanical problem with the truck.
If your model has a fan clutch on the water pump, it may not be working correctly.

It could be the coolant temp sensor which is pretty cheep go to your local parts store and pick one up there also have you changed your thermostat? and are the cooling fans coming on?

check for low coolant, the cooling fan clutch could be faulty it is free wheeling all the time, when engine is hot fan clutch should have some resistance when you turn it by hand. if all is good, your ignition timing could be off,your radiator and engine need flushing out,you could have faulty water pump, a bad egr valve will cause engine over heat if stuck closed which will engine combustion temperature get hotter.make sure you have 50 / 50 antifreeze and water in coolant system too much water in coolant system will cause engine over heat.also radiator pressure cap.check all those things i told you see what happens.

you mention big hills, and other wise no problem, you may be taxing the transmission , have a trans cooler installed, it may cure all your problems, and good for the trans, heat is the trans biggest killer

I think this uses a fluid filled thermally controlled clutch. When the engine is cold, (and OFF), you should be able to move the fan easily by hand. Once the engine has warmed up to normal temp, park it, shut off the engine, and again try to move the fan. It should be very firm compared to when cold. (Don't push too hard on it, you can bend the blades.)

A bad fan clutch usually shows up as overheating during idle and stop-and-go driving, however. At a steady speed of above about 35 MPH, you don't need the fan. So if you are going up the hills at more than 35 MPH, I'd suspect the radiator might be somewhat plugged. You can try having it pressure flushed (that might help) but if not, you might have to replace the radiator. Try to get a higher capacity (more cores) radiator.

under maximium load your cooling system is struggling asuming you have an automatic transmission,it is cooled through the radiator,when running the ac your condenser is hot,right in front of the radiator,if your not leaking,and your anti-freeze looks bright green an clean ,and the fan or fans are working ,first change the thermostat,cheapest,remove the serpintine belt and inspect the water pump pulley,spin it by hand,try to tip it forward and backward,to see if it wobbles,it should spin smooth and quiet,if it has a chattering or growling feel,or the pulley wobbles change the pump,the only thing left is the radiator ,make sure that debri or something isnt stuck in front of it a small piece of paper is enough to restrict airflow,inspect the core is it turning green and the fins are falling out ,is the plastic shroud intact around it, lots of things could be going on ,the transmission could be low on fluid,and running hot,causing the excessive load on the radiator,disregaurd this if you have a manual.need more info to pinpoint further,hope this helps

Radiatior is clogged up, fan clucth defective, thats why when you turn the a/c on the other fan turns on and help the engine to cool down.

It sounds like your coolant level may be too low. When you drive up hill the coolant will tend to flow into your engine block and help to cool it down. When you drive down hill the coolant will tend to flow out of the engine block and into the radiator. This may allow the engine block to overheat. I recommend checking your coolant level. If you need to add coolant use a 50/50 mixture of water and antifreeze. If your coolant level is low you may have a leak. Look for the leak while the engine is hot.

I'd also check to make sure your electric cooling fan is working. Let the engine warm up with the car idling in park. Watch to see if the fan ever turns on. If the fan doesn't turn on the problem could be caused by the fan itself, a fan relay, or a temperature sensor.

If you have seen the signs of leakage around the water pump thn its worth replacing it being that far already.
Its better too, to flush the radiator.
Usually if the seal blows thts the end of the pump even if it looks ok!

is it ever low in coolant? i agree with emissionwiz sounds like your getting airpockets do you have heat when this starts?