GMC Yukon Denali 2006 Manual page 301

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 Combination Weight Rating
(GCWR). See "Weight of the Trailer" later in this 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.
Weight of the Trailer
How heavy can a trailer safely be?
It depends on how you plan to use your rig. For example,
speed, altitude, road grades, outside temperature and
how much your vehicle is used to pull a trailer are all
important. It can also depend on any special equipment
that you have on your vehicle, and the amount of tongue
weight the vehicle can carry. See "Weight of the Trailer
Tongue" later in this section for more information.
Maximum trailer weight is calculated assuming only the
driver is in the tow vehicle and it has all the required
trailering equipment. The weight of additional optional
equipment, passengers and cargo in the tow vehicle
must be subtracted from the maximum trailer weight.
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