Page 97 of 398

Diesel Engine Exhaust Brake
If your vehicle has a DURAMAX®7800 or Caterpillar®
diesel engine, it may have an exhaust brake, which
is located in the exhaust system.
If your vehicle has a 6.6L DURAMAX
®6600 diesel
engine, it may have an exhaust brake, which is
controlled through the turbocharger.
The exhaust brake for both engines operates the same.
The exhaust brake switch
is located in the instrument
panel switchbank.
Push the bottom of the switch to turn the exhaust brake
on. When you push the top of the switch, the exhaust
brake will turn off.
There is an indicator light on the instrument panel
similar to the symbol on the switch, that will come on
when the exhaust brake is active. SeeExhaust
Brake Indicator Light on page 3-41for more information.When using the exhaust brake, the proper gear range
selection is important. The exhaust brake will be
most effective if the gear range selected is the lowest
possible range that does not allow the engine rpm to go
more than 200 rpm above rated (full load) rpm. If you
have a Caterpillar®diesel engine, do not exceed
2900 rpm. If you have a DURAMAX®7800 diesel
engine, do not exceed 2550 rpm. If you have a
DURAMAX
®6600 diesel engine, do not exceed
3600 rpm.
If your vehicle has an Allison
®1000/2200/2300/2500
series automatic transmission and press this button, the
transmission will downshift to a factory default setting
of third gear. To change the default setting, or for more
information on factory default settings, contact your
dealer for assistance.
The accelerator and clutch pedals must be released in
order for the exhaust brake to engage. The exhaust
brake will automatically shut off when the anti-lock brake
system is active.
If your vehicle has a Caterpillar
®diesel engine or a
DURAMAX®6600 diesel engine, the exhaust brake will
become active in cruise control when you exceed
the set speed by 3 to 5 mph.
2-27
Page 99 of 398

Air Shift Control
(Automatic Transmission)
The rear axle shift control
switch for an automatic
transmission is located in
the instrument panel
switchbank.
To use the rear axle shift control, press the bottom of
the switch to get to the high range. The switch indicator
light will come on when the vehicle is in the high
range. Press the top of the switch to return to the low
range.
The two-speed axle should be in low range when
you park the vehicle. You will need to engage the
transmission and move the vehicle a little to assure the
axle is in range. Then shift into PARK (P), apply the
parking brake, and shut off the engine.To shift up from low to high range while driving, press
the bottom of the rear axle shift control switch as you are
releasing the accelerator pedal. After the shift has
occurred, apply the accelerator as desired.
To shift from high to low range while driving, press the
top of the rear axle shift control switch as you release
the accelerator pedal. Press the accelerator pedal slowly
until the down shift has occurred, then apply the
accelerator as desired.
For better performance during off-road or under a heavy
load, shift the axle into low range and then operate
the transmission normally.
For better performance on the highway, shift the axle to
high range and operate the transmission normally.
2-29
Page 100 of 398

Automatic Transmission Operation
We build vehicles with Allison®five and six-speed
automatic transmissions. This part of the manual covers
the basics of these. With these transmissions, you
will find another Allison
®manual in your vehicle that
goes into more detail. On the headliner, in front of and
above the driver, or in some other place near the
driver, you will see a label that describes important
operating facts about the automatic transmission in
your vehicle. Make sure you follow the instructions on
this label.
Be sure to keep your parking brake set until you are
ready to shift into DRIVE (D), and press the brake pedal
while shifting from NEUTRAL (N) or PARK (P) to a
drive gear.
All vehicles equipped with automatic transmissions can
be started in PARK (P), if equipped, or in NEUTRAL (N).
See the Allison
®Transmission Operator’s Manual in
your vehicle for more information about this.
{CAUTION:
It can be dangerous to get out of your vehicle
without the parking brake rmly set. Your
vehicle can roll. If you have left the engine
running, the vehicle can move suddenly. You
or others could be injured. To be sure your
vehicle will not move, even when you are on
fairly level ground, always set the parking
brake.
{CAUTION:
Shifting into a drive gear while your engine is
running at high speed is dangerous. Unless
your foot is rmly on the brake pedal, your
vehicle could move very rapidly. You could
lose control and hit people or objects. Do not
shift into a drive gear while your engine is
running at high speed.
2-30
Page 102 of 398

Eaton®Fuller®Five and Six-Speed
Transmissions and TTC Spicer
Seven-Speed Transmissions
These transmissions have gears that automatically
synchronize when you shift up or down (except
FIRST (1) gear on the five-speed and seven-speed
transmission which is unsynchronized). Choose the gear
that will maintain the road speed you want while
keeping the engine above two-thirds of the governed
speed. When the engine speed drops below two-thirds
of the governed speed, shift into the next lower gear
before your engine begins to lug. When you shift down,
be sure to double-clutch if required.
ZF Six-Speed Transmission
Here is how to operate your transmission.
This six-speed pattern is
unique to GM manual
transmissions.
The transmission always repositions the shift lever to
NEUTRAL, which is located between FOURTH (4)
and FIFTH (5) gear.
To prevent unintentional gear selections, additional force
is required to move the shift lever into REVERSE (R) or
FIRST (1). Use FIRST (1) when trailer towing, driving
with a heavier payload or launching on a grade.
Otherwise, start in SECOND (2) gear. Only shift into
FIRST (1) when the vehicle has stopped moving.
During the first 500 miles (805 km) of vehicle use, start
the vehicle moving in FIRST (1) gear. This allows
the clutch components to wear-in properly.
2-32
Page 110 of 398

Parking
{CAUTION:
If you do not park your vehicle properly, it can
roll. If you have left the engine running, it can
move very quickly. You or others could be
injured. To be sure your vehicle will not move,
even when you are on level ground, follow the
steps below.
Two-Speed Rear Axle
1. With the engine running, shift the two-speed rear
axle into low. To be sure it is in low, you will need
to move the vehicle in gear just a little.
2. Hold the regular brake pedal down with your
right foot.
3. Apply the parking brake.
4. Shift the transmission to NEUTRAL for manual
transmission or PARK (P) for automatic
transmission.
Hydraulic Brakes
(Parking Brake Operation)
If your vehicle has hydraulic brakes, it has either a
parking brake foot pedal or hand lever. If you have the
parking brake foot pedal, it is located below the
instrument panel to the left of the steering column.
If you have the parking brake hand lever, it is located to
the right of the driver, on the floor.Parking Brake Hand Lever Shown
2-40
Page 116 of 398

Running the Engine While Parked
It is better not to park with the engine running. But if you
ever have to, here are some things to know.
{CAUTION:
Idling the engine with the climate control
system off could allow dangerous exhaust into
your vehicle. See the earlier caution under
Engine Exhaust on page 2-45.
Also, idling in a closed-in place can let deadly
carbon monoxide (CO) into your vehicle even if
the climate control fan is at the highest setting.
One place this can happen is a garage.
Exhaust — with CO — can come in easily.
NEVER park in a garage with the engine
running.
Another closed-in place can be a blizzard. See
Winter Driving on page 4-27.
{CAUTION:
It can be dangerous to get out of your vehicle
if the automatic transmission shift lever is not
fully in PARK (P) with the parking brake rmly
set. Your vehicle can roll. Do not leave your
vehicle when the engine is running unless you
have to. If you have left the engine running,
the vehicle can move suddenly. You or others
could be injured. To be sure your vehicle will
not move, even when it is on fairly level
ground, always set the parking brake and
move the automatic transmission shift lever to
PARK (P), or the manual transmission shift
lever to NEUTRAL.
Follow the proper steps to be sure your vehicle will
not move.
2-46
Page 124 of 398
Instrument Panel Overview
Automatic Transmission Shown
3-4
Page 125 of 398

A. Air Outlets. SeeOutlet Adjustment on page 3-24.
B. Instrument Panel Cluster. SeeInstrument Panel
Cluster on page 3-26.
C. Shift Lever. SeeAutomatic Transmission Operation
on page 2-30orManual Transmission Operation
on page 2-31.
D. Air Brake Controls. SeeAir Brake on page 2-42.
E. Transfer Case Controls (If Equipped). See
Four-Wheel Drive on page 2-35. Air Filter Gage
(If Equipped). SeeAir Filter Restriction Indicator on
page 3-46.
F. Auxiliary Gages. SeeWarning Lights, Gages, and
Indicators on page 3-25.
G. Exterior Lamp Control. SeeExterior Lamps on
page 3-14.H. Turn Signal/Multifunction Lever. SeeTurn
Signal/Multifunction Lever on page 3-7.
I. Hazard Warning Flashers Button. SeeHazard
Warning Flashers on page 3-6.
J. Audio System(s). SeeAudio System(s) on
page 3-48.
K. Climate Controls. SeeClimate Control System on
page 3-20.
L. Instrument Panel Switchbank. SeeInstrument Panel
Switchbank on page 3-18.
M. Airbag Off Switch. SeeAirbag Off Switch on
page 1-58.
N. Accessory Power Outlets. SeeAccessory Power
Outlet(s) on page 3-19.
3-5