Dodge Ram Truck 2008 Owner's Manual page 304

302 STARTING AND OPERATING
When operating your vehicle in 4WD LO, the engine
speed is approximately three times that of the 2WD, 4WD
AUTO or 4WD HI positions at a given road speed. Take
care not to overspeed the engine and do not exceed 25
mph (40 km/h).
Proper operation of 4-wheel drive vehicles depends on
tires of equal size, type and circumference on each wheel.
Any difference in tire size can cause damage to the
transfer case.
Because 4-wheel drive provides improved traction, there
is a tendency to exceed safe turning and stopping speeds.
Do not go faster than road conditions permit.
WARNING!
You or others could be injured if you leave the
vehicle unattended with the transfer case in the
NEUTRAL position without first fully engaging the
parking brake. The transfer case NEUTRAL position
disengages both the front and rear driveshafts from
the powertrain and will allow the vehicle to move
regardless of the transmission position. The parking
brake should always be applied when the driver is
not in the vehicle.