The Intake Air Temperature (IAT) sensor on a 2007 Chevy Silverado (new body style) is located within the intake air duct, typically
before the throttle body. It's usually a small, temperature-sensing element incorporated into the air intake tubing itself. You'll likely need to trace the intake tubing from the air filter housing towards the throttle body to find it. It's often a small sensor with a single or a couple of wires connected to it.
It's difficult to give a more precise location without knowing the exact engine configuration (4.3L, 4.8L, 5.3L, 6.0L etc.), but the general area described above is where you should look. A repair manual specific to your truck's year and engine would provide the most accurate location.
