2010 GMC Sierra 1500 Crew Cab Owner's Manual - Page 426

Four-Wheel-Drive Vehicles { WARNING: Shifting a four-wheel-drive vehicle's transfer case into N (Neutral) can cause the vehicle to roll even if the transmission is in P (Park). The driver or others could be injured. Make sure the parking brake is firmly set before the transfer case is shifted to N (Neutral). 4. Shift the transfer case to N (Neutral). See "Shifting into Neutral" under Four-Wheel Drive on page 3‑39 for the proper procedure to select the Neutral position for the vehicle. Use the following procedure to dinghy tow a four-wheel-drive vehicle: 1. Position the vehicle being towed behind the tow vehicle and shift the transmission to P (Park). 2. Turn the engine off and firmly set the parking brake. 3. Securely attach the vehicle being towed to the tow vehicle. 5. Release the parking brake only after the vehicle being towed is firmly attached to the towing vehicle. 6. Turn the ignition to LOCK/OFF and remove the key - the steering wheel will still turn. After towing, see "Shifting Out of Neutral" under Four-Wheel Drive on page 3‑39 for the proper procedure to take the vehicle out of the Neutral position. 5-50