GMC 2010 Yukon/Yukon XL Owner's Manual page 404

Two-wheel-drive vehicles and four-wheel drive vehicles
with a single speed automatic transfer case should
not be towed with all four wheels on the ground.
Two-wheel-drive transmissions have no provisions for
internal lubrication while being towed. Four-wheel drive
vehicles with a single speed automatic transfer case
have no neutral position and will spin the transmission
when the rear wheels turn.
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