To find it precisely, you'll need to:
* Consult a repair manual: A shop manual specific to your year, make, model, and transmission will give you the most accurate location and diagrams.
* Use a parts diagram: Many online auto parts stores (like AutoZone, Advance Auto Parts, etc.) allow you to look up diagrams for your vehicle's transmission, showing the sensor's position.
* Visual inspection: With the truck safely secured (on jack stands, etc.), carefully inspect the driver's side of the transmission. The sensor is usually a relatively small, cylindrical component with a wire harness connected to it.
Caution: Working under a vehicle can be dangerous. Always use jack stands, and follow proper safety procedures. If you're not comfortable performing this yourself, take it to a qualified mechanic.
