Don’t know if it applies to GMCs or not, but the Chevy trucks used the same key for ignition, door, and glovebox locks. At least that’s what the owner’s manual states.
The key code can be found by removing the door lock and looking where the lock shaft attaches to the cylinder. There’s also a code number stamped on the ignition cylinder, but you need a key to get the cylinder out.
Guitplayer is the guy to contact about key cutting.
