GMC 2006 Sierra 1500 Pickup Owner's Manual page 134

An indicator light near the lever shows you the transfer
case settings:
Notice: Driving on clean, dry pavement in
four-wheel drive for an extended period of time may
cause premature wear on your vehicle's powertrain.
Do not drive on clean, dry pavement in four-wheel
drive for extended periods of time.
4L (Four-Wheel Low): This setting also engages your
front axle and delivers extra torque. You may never need
4L. It sends maximum power to all four wheels. You might
choose 4L if you are driving off-road in deep sand, deep
mud, deep snow, and while climbing or descending steep
hills. When operating in Four-Wheel Low, the gear ratio
provides additional torque when compared to four-wheel
high. The transmission gear shift feel will be exaggerated.
CAUTION:
{
Shifting the transfer case to NEUTRAL
can cause your vehicle to roll even if the
transmission is in PARK (P), or if you have a
manual transmission, even if you are in gear.
You or someone else could be seriously injured.
Be sure to set the parking brake before placing
the transfer case in NEUTRAL. See Parking
Brake on page 2-52.
2-40
N (Neutral): Shift to this setting only when your vehicle
needs to be towed. See Recreational Vehicle Towing
on page 4-62 or Towing Your Vehicle on page 4-62.
2H (Two-Wheel High): This setting is used for driving in
most street and highway situations. Your front axle is not
engaged in two-wheel drive. This setting also provides
the best fuel economy.
4H (Four-Wheel High): Use this setting when you need
extra traction, such as on snowy or icy roads or in most
off-road situations. This setting also engages your front
axle to help drive your vehicle. This is the best setting to
use when plowing snow.
You can shift from 2H to 4H or 4H high to 2H while the
vehicle is moving. Your front axle will engage faster if
you take your foot off of the accelerator for a couple of
seconds after you shift. In extremely cold weather,
it may be necessary to stop or slow the vehicle to shift
into four-wheel high.