GMC 2006 Sierra - Manual (Page 411)

All engine speed values listed above are factory preset
values. With the exception of the TCC lockup speed
(1,100 rpm) and the “tap” increment (100 rpm), all of
these values are programmable and can be adjusted by
your dealer or body upfitter. If the PTO software settings
do not match the settings shown here, then they may
have already been altered in order to satisfy the
requirements of the installed PTO system and body
equipment.
When the PTO switch is turned on, the engine is limited
to 2,200 rpms. If there are no accessories installed
on the vehicle, make sure the PTO switch is turned off.
Step-Bumper Pad
Your vehicle has a rear step bumper with a rear step
pad at the center of the bumper.
If you will be using the
bumper to tow a trailer,
and your step-bumper has
three cutout circles, you
must push out the center
cutout circle to install the
trailer ball.
If your step-bumper has only one cutout circle, you
will have to cut out the circle, then remove it to install
the trailer ball.
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