GMC 2007 Acadia Owner's Manual page 132

When you shift from DRIVE (D) to LOW (L), the
transmission will shift to a pre-determined
lower gear range. The highest gear available for
this pre-determined range is displayed next to
the L in the DIC. See Driver Information Center
(DIC) on page 232 and DIC Operation and
Displays (With DIC Buttons) on page 233 or DIC
Operation and Displays (Without DIC Buttons)
on page 239 for more information. The number
displayed in the DIC is the highest gear that
the transmission will be allowed to operate in.
However, your vehicle can automatically shift to
lower gears as required by various driving
conditions. This means that all gears below that
number are available. For example, when
FOURTH (4) is shown next to the L, FIRST (1)
through FOURTH (4) gears are automatically
shifted by the vehicle. You cannot shift into
FIFTH (5) until the plus (+) button is used or you
shift back into DRIVE (D) mode.
132
While in LOW (L), the transmission will prevent
shifting to a lower gear range if the engine speed
is too high for the gear range you are trying to
select. You have a brief period of time to slow the
vehicle speed. If vehicle speed is not reduced
within the timeframe allowed, the lower gear range
attempted will not be available. The highest
possible gear that is allowed for that engine speed
will display next to the L in the DIC. Try again
to slow the vehicle speed and press the minus (−)
button to the desired lower gear range.
Automatic Engine Grade braking is not available
when the ERS is active. It is available in
DRIVE (D) for both normal and Tow/Haul mode.
While using the ERS, cruise control and the
tow/haul mode can be used. See Tow/Haul Mode
on page 133 for more information.