GMC 2004 Sierra 1500 Pickup Owner's Manual page 109

To remove the tailgate, do the following:
1. Raise the tailgate
slightly and release
both retaining
cable clips. To release
the retaining cable
clips, lift the cable so it
points straight out
and push the cable clip
forward.
Reverse the above procedure to reinstall. Make sure the
tailgate is secure.
2. With the tailgate at a
slight upward angle,
pull back on the tailgate
at the right edge and
then move the
tailgate to the right to
release the left edge.
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