GMC 2005 Sierra 1500 Pickup, Owner'S Manual, Page: 120 / 574

Tow/Haul is a feature on automatic transmission
equipped vehicles that assists when pulling a heavy
trailer or large or heavy load. Tow/Haul mode adjusts the
transmission’s shift pattern to reduce shift cycling,
providing increased performance, vehicle control, and
transmission cooling when towing or hauling heavy loads.
If your vehicle is equipped with an Allison
®
transmission,
you may have both Tow/Haul mode and overdrive
disable. See “Tow/Haul Mode” under Towing a Trailer
on page 4-68 for more information.
Grade Braking
(Allison Transmission
®
Only)
Grade braking uses the engine and transmission to slow
a loaded vehicle on hills in addition to using the
brakes, saving on brake wear and increasing vehicle
stability. The Allison Transmission
®
, when sensing
the driver’s desire to slow down while driving downhill,
will automatically shift to the next lower gear range
to assist in slowing down the vehicle. Grade braking is
active and automatic both in Tow/Haul mode and
normal shift mode. Grade braking is more aggressive
when in Tow/Haul mode and can automatically downshift
to SECOND (2), which is different than grade braking
while in normal shift mode where automatic downshifts
are limited to FOURTH (4).
The tachometer for both the diesel and gasoline engine
shows a dashed red zone and a solid red zone. The
dashed red zone indicates where a transmission
shift occurs for full engine power. When using grade
braking, the transmission’s shift point is adjusted to just
prior to the solid red zone, providing the benefit of
additional engine braking.
Grade braking driving within the dashed red zone is
normal, both the diesel and gasoline engine have been
designed for this grade braking feature. Do not allow
the engine to go into the solid red zone. Apply the
vehicle’s brakes for a short time to slow down if you are
driving on a long hill and the tachometer needle
enters the solid red zone. See Towing a Trailer on
page 4-68 for more information.
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