GMC Sierra 2010 Owner's Manual page 174

WARNING:
Shifting the transfer case to Neutral can cause
the vehicle to roll even if the transmission is in
P (Park). 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 3 50.
3-38
A parking brake symbol
is located next to the
N (Neutral) symbol as a
reminder to set the
parking brake before
shifting the transfer case
into N (Neutral).
N (Neutral) : Shift to this setting only when the vehicle
needs to be towed. See Recreational Vehicle Towing on
page 5 43 or Towing Your Vehicle on page 5 43.
2 (Two-Wheel-Drive High): This setting is used for
driving in most street and highway situations. The front
axle is not engaged in two-wheel drive. This setting also
provides the best fuel economy.
4 (Four-Wheel-Drive 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
the front axle to help drive your vehicle. This is the best
setting to use when plowing snow.
You can shift from Two-Wheel-Drive High to
Four-Wheel-Drive High or Four-Wheel-Drive High to
Two-Wheel-Drive High while the vehicle is moving.
In extremely cold weather, it may be necessary to stop
or slow the vehicle to shift into Four-Wheel-Drive High.