You don't have a timing belt, its a chain and shouldn't need to be replaced any time soon. To check the pump, listen for any squealing from the front of the engine that increases with speed. There should also be a weep hole at the bottom of the pump. If the bearings or seals are going bad that weep hole will have green, flaky stuff running off below. If you see that and hear the squealing, its time to replace the water pump.
Also, check the radiator and make sure that its clear of mud and debris. You can remove your cap (when cool) and let the engine run. If the pump and thermostat are working, you will be able to see waterflow across the top tank when the truck reaches operating temperature.