Does it squeak sitting still? I would check the serpentine belt, tension pulley, idler pulleys, and look for signs of coolant leaking from the water pump under the front of the truck. More than likely you will find the squeak on the front of the engine. If you can hear it there but can't pin point it, find yourself a "Stethoscope probe" to touch to the mounting bolts for the pulleys holding the belt on and listen through each of them. BE CAREFUL not to get it into the fan while the engine is running. But doing this, when you find the source you will know it by the sound through the probe.
That is if it squeaks while sitting still.