2001 GMC Sierra 1500 Pickup Owner's Manual - Page 306

Variable Mode: PTO speed control mode can be used for both stationary and mobile applications. This mode allows PTO to be controlled in a fashion similar to how cruise control sets vehicle speed. The operator can set to an rpm (between 800 and 2200) with the cruise control feature or with the SET position on the PTO switch. The operator is then able to increase engine speed in 100 rpm increments with the resume position on the cruise control. The operator can also decrease engine speed in 100 rpm increments with either the SET position on the cruise control or the PTO switch. Vehicles not equipped with cruise control will not have the resume capability. All engine speed values listed above are factory preset values. With the exception of the TCC lockup speed (1100 rpm) and the "tap" increment (100 rpm), all of these values are programmable and can be adjusted by your GM 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. 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. 4-84