1. Sit in the driver's seat of your GM truck and close all of the vehicle's doors behind you.
2. Slide your key into the ignition cylinder. Press and hold the "Unlock" button on the control panel of the driver's-side door.
3. Continue to hold down the "Unlock" button. Toggle the key between the "On" and "Off" ignition positions. Follow this sequence, maintaining a rapid, yet even, pace: "On," "Off," "On," "Off."
4. Release the "Unlock" button; the truck's power locks will cycle to indicate that the programming mode has been successfully accessed.
5. Press and hold the "Lock" and "Unlock" buttons on the GM key fob until the power locks perform a second automatic locking cycle.
6. Turn the key to the "On" ignition position to exit the key fob programming mode.