To be certain, you should:
* Consult your owner's manual: This is the best resource for the specific location on your truck.
* Look for a small, roughly cylindrical component: It will have vacuum lines connected to it.
* Use a diagram: Online parts diagrams for your specific year, make, model, and engine will show the location. Use the VIN number to ensure you have the correct diagram.
Without knowing the engine type, a precise location can't be given. The visual inspection guided by the above points will be the most reliable method.