GMC Yukon Owner's Manual page 418

Tow/Haul Mode
Tow/Haul is a feature that assists when pulling a heavy
trailer or a large or heavy load. See Tow/Haul Mode on
page 3 39 for more information.
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Pressing this button
at the end of the shift
lever turns on and off
the tow/haul mode.
This indicator light on
the instrument panel
cluster comes on when
the tow/haul mode is on.
Tow/Haul is designed to be most effective when
the vehicle and trailer combined weight is at least
75 percent of the vehicle's Gross Combined Weight
Rating (GCWR). See Weight of the Trailer earlier in
the section. Tow/Haul is most useful under the following
driving conditions:
When pulling a heavy trailer or a large or heavy
load through rolling terrain.
When pulling a heavy trailer or a large or heavy
load in stop and go traffic.
When pulling a heavy trailer or a large or heavy
load in busy parking lots where improved low
speed control of the vehicle is desired.
Operating the vehicle in Tow/Haul when lightly loaded
or with no trailer at all will not cause damage. However,
there is no benefit to the selection of Tow/Haul when the
vehicle is unloaded. Such a selection when unloaded
may result in unpleasant engine and transmission
driving characteristics and reduced fuel economy.
Tow/Haul is recommended only when pulling a heavy
trailer or a large or heavy load.