WARNING: This page is about a different car, the 2002 GMC Yukon XL, 2002 GMC Sierra, 2002 Chevrolet Suburban, and 2002 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Tow/Haul Mode System Wiring Diagram (Sierra, Sierra HD, Silverado, Silverado HD, Suburban & Yukon XL)
Courtesy of GENERAL MOTORS CORP.
Fig 2: Transmission Electronic Control System Wiring Diagram (Sierra, Sierra HD, Silverado, Silverado HD, Suburban & Yukon XL - 6.0L)
Fig 3: Transmission Electronic Control System Wiring Diagram (Avalanche, Suburban & Yukon XL - 8.1L)