Has anyone had to change a thermostat on a 4.7L Dodge Pickup? Even when my truck has warmed up, the air still blows cold. When you rev the engine, then the air will get warm for a few seconds and then blow cold again. Also, where is the thermostat located?

Check coolant level and inspect for leaks.
Here's a diagram of your vehicles t-stat:

Attachment 5706

I hope this helps.