GMC 2010 Yukon XL Denali Owner's Manual page 368

All-Wheel-Drive Vehicles
Dinghy and Dolly Towing
5-38
Towing an all-wheel-drive vehicle with all
four wheels on the ground, or even with only two of
its wheels on the ground, will damage drivetrain
components. Do not tow an all-wheel-drive vehicle
with any of its wheels on the ground.
All-wheel-drive vehicles are not designed to be towed
with any wheels on the ground. If the vehicle must be
towed, see Towing Your Vehicle previously.