2005 GMC Sierra 1500 Pickup Owner's Manual - Page 361

Trailer Recommendations {CAUTION: Shifting a four-wheel-drive vehicle's transfer case into NEUTRAL can cause your vehicle to roll even if the transmission is in Park (P) for an automatic transmission, or if your vehicle is in gear, for a manual transmission. You or others could be injured. Make sure the parking brake is firmly set before you shift the transfer case to NEUTRAL. 5. Shift the transfer case to NEUTRAL. See Four-Wheel Drive on page 2-37. 6. Release the parking brake only after the vehicle being towed is firmly attached to the tow vehicle. 7. Turn the ignition to LOCK. You must subtract your hitch loads from the CWR for your vehicle. Weigh your vehicle with the trailer attached, so that you won't go over the GVWR or GAWR. If you are using a weight-distributing hitch, weigh the vehicle without the spring bars in place. You'll get the best performance if you spread out the weight of your load the right way, and if you choose the correct hitch and trailer brakes. For more information, see Towing a Trailer on page 4-68. 4-67