Chevrolet 2006 Avalanche Owner's Manual page 88

3. While holding the rear glass in place, press the
glass-catch release button (C) and pull the top of
the rear glass toward you using the grab
handle(s) (B) located at the top of the rear glass.
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4. With the rear glass tilted toward you, lift it out from
the lower window frame channel. Use the grab
handles to assist you in removing the rear glass.