On a 1999 Silverado 2500 with the 6.0L Vortec engine, the crankshaft position sensor (CKP) is located on the
passenger side of the engine block,
near the rear of the engine (towards the transmission). It's usually mounted in a fairly accessible location, but you'll likely need to look between the engine block and the transmission to spot it. It's a small sensor with a single wire connector.
Keep in mind that exact placement can vary slightly depending on specific engine configurations and any aftermarket modifications. A repair manual specific to your vehicle year and engine would give the most precise location.
