GMC 1999 Sierra 1500 Pickup Owner's Manual page 108

Features & ContmIs
Sliding Rear Window
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K2230
Your vehicle may have a sliding rear window. To open the window, pull the
driver's side of the latch forward and
move it toward the passenger side.
Slide the window open. When you close the windows, hook the latch on the
passenger side window and press the driver's side rearward firmly. Be sure
the latch catches.
Swing-Out Windows (Extended Cab)
K2231
If your vehicle has rear swing-out windows, just unlatch them at their clasps
and push out on the glass to open them.
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