GMC Yukon 2007 Owner's Manual page 424

Dinghy Towing
Two-Wheel-Drive Vehicles
Notice: If you tow a two-wheel-drive
vehicle with all four wheels on the ground, the
transmission could be damaged. The repairs
would not be covered by your warranty.
Do not tow a two-wheel-drive vehicle with all
four wheels on the ground.
Two-wheel-drive vehicles should not be
towed with all four wheels on the ground.
Two-wheel-drive transmissions have no provisions
for internal lubrication while being towed.
424
Four-Wheel-Drive Vehicles
Use the following procedure to tow your vehicle:
1. Shift the transmission to PARK (P).
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.