GMC 2010 Sierra 1500 Crew Cab Owner's Manual page 427

Two-wheel-drive vehicles should not be towed with
the rear wheels on the ground. Two-wheel-drive
transmissions have no provisions for internal lubrication
while being towed.
To dolly tow a two wheel drive vehicle, the vehicle must
be towed with the rear wheels on the dolly. See Rear
Towing (Rear Wheels Off the Ground) later in this
section for more information.
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