GMC Sierra Classic 2007 Owner's Manual page 419

Four-Wheel-Drive Vehicles
Use the following procedure to tow your vehicle:
1. Shift an automatic transmission to PARK (P),
or a manual transmission to FIRST (1).
2. Turn the engine off, but leave the ignition on.
3. Firmly set the parking brake.
4. Securely attach the vehicle being towed to the
tow vehicle.
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 151 for the
proper procedure to select the neutral position
for your vehicle.
6. Release the parking brake only after the
vehicle being towed is firmly attached to
the towing vehicle.
7. Turn the ignition off and leave the steering
column unlocked.
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