Q&A

 Master

It could be so many things. First, check the level in your radiator AFTER your truck has cooled off. If it is low, you may have a leak some where i.e from the water pump or a hose clamp etc.
When was the last time you replaced your thermostat and serviced your cooling system? A thermostat really lasts about 60k. Coolant about 30k, I know say they go forever, but then people ruin their engines because the basic servicing has been ignored BECAUSE of the "100k" before you have to touch anything mentality.