It is recommended to unplug the negative battery cable before you start performing this repair, specially since you will be working near the alternator, once the negative battery cable has been disconnected, proceed to drain the engine coolant by loosening the drain valve located at the bottom of the radiator, next, remove the bolt that attaches the alternator bracket to the intake manifold. ( see image )
Next, remove the small bolt from the AC line bracket.
Remove the nut that fasten the AC bracket to the stud and remove it from the vehicle, loosen the stud and move the alternator bracket away from the upper radiator hose.
Using a long extension and a 1/2'' socket remove the two water outlet bolts, pull the upper radiator hose up away from the intake manifold.
Using channel lock pliers, slide the hose clamp away from the water outlet and separate it from the upper radiator hose.
Remove the old thermostat using long needle nose pliers.
Scrape the old gasket material from the water outlet and the thermostat cavity in the intake manifold, place a rag inside the water passage to avoid dropping gasket particles inside the cooling system.
Once you are done removing the old gasket from the intake manifold and the water outlet, proceed to install the new thermostat, it is recommended to apply a light coat of RTV silicone to fill the imperfections and provide a perfect seal.
Install the new thermostat gasket while the silicone is still wet.
Install the water outlet back inside the upper radiator hose,apply a light coat of gray silicone and place it on the intake manifold making sure that the bolt holes are aligned.
Use a tool similar to the one on the picture to install the water outlet bolts and to turn them a couple of turns, finish tighten them up with the same socket and extension you used to take them off.
Install the remaining items in the reverse order they were removed, add new 50/50 coolant mix to the cooling system, install the radiator cap on , make sure that all your tools are out of the way and start the engine, place close attention to the water temperature gauge, if you see it starting to go past half way turn the engine off, loosen the radiator cap slowly to vent the pressure, once the pressure has been released remove the radiator cap and add the necessary coolant to the system, install the radiator cap back on and start the engine again, you may have to repeat these steps more than once in order to remove all the air from the system, otherwise you will cause the engine to build excessive pressure and you could damage your heater core, once the thermostat opens and the air has been bled from the system take the truck for a test drive, on your return inspect for leaks, if there aren't any you are done.