Transmission Control Module (TCM)
WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, and 2009 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The TCM adjusts shift patterns to minimize shift during PTO operation. The TCM also provides transmission gear states and temperature conditions to the PTOM via serial data messages.