GMC Sierra 2000 Owner's Manual page 235

Step-Bumper Pad
If your vehicle has a rear step bumper, it may be
equipped with a rear step pad at the center of
the bumper.
If you will be using the
bumper to tow a trailer,
you must remove the
center cutout circle to install
the trailer ball. You must
also remove both outer
cutouts to attach the trailer
safety chains.
To remove the pad, lift the
edge of the pad from the
rear of the bumper and
swing it forward. When
the pad releases from the
bumper holes, lift the
pad off.
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