It's mounted in the top of the cam syncronizer.
Passenger side , toward the firewall , on top.
Similar to the old distributors.
If you have a higher mileage truck , go to the dealer and get a new syncro assembly. Cost ~ $200
These are a known failure part and can do major engine damage when they go bad , as they also drive the oil pump.
Use the search button at the top of the pane and enter 'cam syncro'.
Many posts about this problem.