The IAT Sensor is located on the #2 Intake Runner (3.9/5.2/5.9L) or under the Throttle Body, in the manifold (4.7L) - Big Brass looking sensor with two wires (Grayish connector)
Remove the IAT sensor from the manifold and plug the hole with a 1/4" NPT Pipe Plug (Home Depot)
Drill a 1/2" hole in the intake tube and thread the IAT sensor into the hole (use some silicone if you want...not required though) - You may have to extend the wires about 6-12" in some cases (use 16ga. wire)
Here's the theory. The air temp is higher in the intake manifold than up stream somewhere like the intake tube or airhat. When relocated, the sensor sends the computer data that indicates the air temp is colder/denser. The computer compensates for the colder air by allowing more fuel to flow thru the injectors.
FWIW, it seems that this mod works better on some trucks than others. If you plan on doing it, it is best to add a second sensor and keep the original one in place. This allows you to switch back and forth which is especially handy during the winter.