Removal Procedure

Remove the tail lamp. Refer to TAIL LAMP REPLACEMENT (PICKUP) or TAIL LAMP REPLACEMENT (UTILITY) in EXTERIOR LIGHTS article.
Perform the following steps in order to remove the pickup box endgate cable from the striker bolt:
1. 2.1
  
  Open the endgate.
2. 2.2
  
  Safely support the endgate.
3. 2.3
  
  Disconnect the slotted hole at the end of the cable from the endgate striker bolt.
Remove the nuts and bolts that retain the pickup box endgate striker to the vehicle.
Remove the pickup box endgate striker from the vehicle.

Fig 1: Locating Pickup Box Endgate Striker (Pickup)
Courtesy of GENERAL MOTORS CORP.