Chevrolet 2003 Silverado 1500 Pickup Owner's Manual page 115

Drive (D) can be used when towing a trailer, carrying a
heavy load, driving on steep hills or for off-road
driving. You may want to shift the transmission to
THIRD (3) or, if necessary, a lower gear selection if the
transmission shifts too often.
Notice: If your vehicle is equipped with the
Allision@ Transmission, do not idle in DRIVE (D) for
more than five minutes. Extended idling in
DRIVE (D) may cause transmission overheating and
damage. Always select PARK (P) if idle time is
longer than five minutes.
If your vehicle is equipped with the Allison@
Transmission, it will initially attain first range when
DRIVE (D) is selected. As vehicle speed increases, the
transmission will upshift automatically through each
available range up to FIFTH (5). As the vehicle slows,
the transmission will downshift automatically.
THIRD ( 3 ) : This position is also used for normal driving,
however it offers more power and lower fuel economy
than DRIVE (D).
SECOND (2): This position gives you more power but
lower fuel economy. You can use SECOND (2) on
hills. It can help control your speed as you go down
steep mountain roads, but then you would also want to
use your brakes off and on.
If you manually select SECOND (2) in a light duty
automatic transmission, the transmission will drive in
second gear. You may use this feature for reducing the
speed of the rear wheels when you are trying to start
your vehicle from a stop on slippery road surfaces.
FIRST (1): This position gives you even more power
(but lower fuel economy) than SECOND (2). You
can use it on very steep hills, or in deep snow or mud.
If the selector lever is put in FIRST (1) while the
vehicle is moving forward, the transmission won't shift
into first gear until the vehicle is going slowly enough.
Notice: If your rear wheels won't turn, don't
try to drive. This might happen if you were stuck in
very deep sand or mud or were up against a solid
object. You could damage your transmission. Also,
if you stop when going uphill, don't hold your
vehicle there with only the accelerator pedal. This
could overheat and damage the transmission.
Use your brakes or shift into PARK (P) to hold your
vehicle in position on a hill.
On cold days, approximately 32°F (OOC) or colder, your
transmission is designed to shift differently until the
engine reaches normal operating temperature. This is
intended to improve heater performance.
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