GMC 2010 Savana 1500 Cargo Owner's Manual page 132

D (Drive): This position is for normal driving. It provides
the best fuel economy. If you need more power for
passing, and you are:
•
Going less than about 35 mph (55 km/h), push the
accelerator pedal about halfway down.
•
Going about 35 mph (55 km/h) or more, push the
accelerator all the way down.
By doing this, the vehicle shifts down to the next
gear and has more power.
D (Drive) can be used when towing a trailer, carrying a
heavy load or driving on steep hills. You might want
to shift the transmission to a lower gear selection if the
transmission shifts too often.
Downshifting the transmission in slippery road conditions
could result in skidding. See Skidding under Loss of
Control on page 5-9.
The vehicle has a shift stabilization feature that adjusts
the transmission shifting to the current driving conditions
in order to reduce rapid upshifts and downshifts. This shift
stabilization feature is designed to determine, before
making an upshift, if the engine is able to maintain vehicle
speed by analyzing things such as vehicle speed, throttle
position, and vehicle load. If the shift stabilization feature
determines that a current vehicle speed cannot be
maintained, the transmission does not upshift and instead
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holds the current gear. In some cases, this could appear
to be a delayed shift, however the transmission is
operating normally.
The transmission uses adaptive shift controls.
Adaptive shift controls continually compares key shift
parameters to pre-programmed ideal shifts stored in the
transmissions computer. The transmission constantly
makes adjustments to improve vehicle performance
according to how the vehicle is being used, such as with
a heavy load or when temperature changes. During this
adaptive shift control process, shifting might feel different
as the transmission determines the best settings.
The shift quality of a new vehicle may not be ideal
because the Adaptive Shift Control process may not
have determined the best settings for a particular shift
or condition. Shift quality will improve with continued
driving.
When temperatures are very cold, the transmission's
gear shifting could be delayed providing more stable
shifts until the engine warms up. Shifts could be more
noticeable with a cold transmission. This difference
in shifting is normal.
M (Manual Mode): This position lets drivers select
the range of gears appropriate for current driving
conditions. If the vehicle has this feature, see Range
Select Mode later in this section.