2004 GMC Sierra 1500 Pickup Owner's Manual - Page 399

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 2200 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. 4-103