GMC 2005 Sierra 1500 Pickup Owner's Manual page 363

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Then, during the first 500 miles (800 km) that you
tow a trailer, don't drive over 50 mph (80 km/h)
and don't make starts at full throttle. This helps your
engine and other parts of your vehicle wear in at
the heavier loads.
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If you have an automatic transmission, you can tow
in DRIVE (D). You may want to shift the
transmission to THIRD (3) or, if necessary, a lower
gear selection if the transmission shifts too often,
such as under heavy loads and/or hilly conditions.
If you have a manual transmission and you are
towing a trailer, it's better not to use the highest
gear. See Tow/Haul Mode Light on page 3-49.
Three important considerations have to do with weight:
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The weight of the trailer
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The weight of the trailer tongue
•
The weight on your vehicle's tires
Tow/Haul Mode
Tow/Haul is a feature on automatic transmission
equipped vehicles that assists when pulling a heavy
trailer or a large or heavy load. Tow/Haul mode adjusts
the transmission's shift pattern to reduce shift cycling
(rapid up and downshifts/gear hunting), providing
increased performance, vehicle control, and transmission
cooling when towing or hauling heavy loads.
Automatic transmission equipped vehicles are provided
with a button at the end of the shift lever which when
pressed enables Tow/Haul. When the button is pressed,
a light on the instrument panel will illuminate to
indicate that Tow/Haul has been selected. Tow/Haul
may be turned off by pressing the button again, at which
time the indicator light on the instrument panel will
turn off. The vehicle will automatically turn off Tow/Haul
every time it is started.
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" later 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.
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