Removal Procedure

Remove the rear body side trim panel. Refer to TRIM PANEL REPLACEMENT - BODY SIDE (STANDARD CAB PICKUP) , TRIM PANEL REPLACEMENT - BODY SIDE (EXTENDED CAB PICKUP) , TRIM PANEL REPLACEMENT - BODY SIDE (2-DOOR UTILITY) , TRIM PANEL REPLACEMENT - BODY SIDE (4-DOOR UTILITY) and TRIM PANEL REPLACEMENT - BODY SIDE (CREW CAB) in INTERIOR TRIM article.
Disconnect the electrical connectors.
Remove the radio rear speaker nuts.

Fig 1: Locating Rear Speaker Components (Pickup)
Courtesy of GENERAL MOTORS CORP.
Remove the rear speaker from the rear body side trim panel.