
Passlock®
Your vehicle is equipped with the Passlock®
theft-deterrent system.
Passlock
®is a passive theft-deterrent system.
Passlock®enables fuel if the ignition lock cylinder is
turned with a valid key. If a correct key is not used or the
ignition lock cylinder is tampered with, fuel is disabled.
If the engine stalls and the security light ashes,
wait until the light stops ashing before trying to restart
the engine. Remember to release the key from
START as soon as the engine starts.
If the engine is running and the security light comes on,
you will be able to restart the engine if you turn the
engine off. However, your Passlock
®system is
not working properly and must be serviced by your
dealer. Your vehicle is not protected by Passlock
®at
this time. You may also want to check the fuse.
SeeFuses and Circuit Breakers on page 5-123.
See your dealer for service.
In an emergency, call the GM Roadside Assistance
Center. SeeRoadside Assistance Program on page 7-6.
Starting and Operating
Your Vehicle
New Vehicle Break-In
Notice:Your vehicle does not need an elaborate
break-in. But it will perform better in the long run if
you follow these guidelines:
Keep your speed at 55 mph (88 km/h) or less for
the rst 500 miles (805 km).
Do not drive at any one speed, fast or slow,
for the rst 500 miles (805 km). Do not make
full-throttle starts.
Avoid making hard stops for the rst 200 miles
(322 km) or so. During this time your new brake
linings are not yet broken in. Hard stops with new
linings can mean premature wear and earlier
replacement. Follow this breaking-in guideline
every time you get new brake linings.
Do not tow a trailer during break-in. SeeTowing a
Trailer on page 4-69for more information.
2-21

Automatic Transmission Operation
If your vehicle is equipped with an automatic
transmission, it features an electronic shift position
indicator within the instrument panel cluster. This display
must be powered anytime the shift lever is capable of
being moved out of PARK (P). SeeFuses and
Circuit Breakers on page 5-123.
There are several different positions for your shift lever.
PARK (P):This position locks your rear wheels. It is the
best position to use when you start your engine because
your vehicle cannot move easily. If your vehicle is
equipped with the Allison Transmission
®, use PARK (P)
for stationary operation of the Power Takeoff (PTO),
if equipped. The Allison Transmission
®is equipped
with park pawl designed to hold the higher weight of
commercial medium duty trucks. Therefore, the Allison
Transmission
®uses larger parts than other automatic
transmission. These larger parts may sometimes make a
clunk noise when the selector lever is moved from
DRIVE (D) or REVERSE (R) to PARK (P). This is normal
and there is no damage occurring during these shifts.
{CAUTION:
It is dangerous to get out of your vehicle if the
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 you are on fairly level ground, always set
your parking brake and move the shift lever to
PARK (P). SeeShifting Into Park (P) (Automatic
Transmission) on page 2-52. If you are pulling
a trailer, seeTowing a Trailer on page 4-69.
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DRIVE (D):This position is for normal driving. If you
need more power for passing, and you are:
Going less than about 35 mph (55 km/h), push your
accelerator pedal about halfway down.
Going about 35 mph (55 km/h) or more, push the
accelerator all the way down.
You will shift down to the next gear and have more
power.
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.
If your vehicle is equipped with the Allison
Transmission
®, it will initially attain rst 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.
The Allison Transmission
®uses a shift stabilization
feature to adjust the transmission shift schedule to the
current driving situation to reduce rapid upshifts and
downshifts. This shift stabilization feature is designedto determine before making an upshift if the engine will
be able to maintain vehicle speed by analyzing things
such as throttle position, vehicle load, and hill grade.
If the shift stabilization feature determines that current
vehicle speed cannot be maintained, the transmission
does not upshift and instead holds the current gear.
In some cases, this may appear to be a hanging shift,
however the transmission is operating normally.
The Allison Transmission
®also uses adaptive shift
controls. Adaptive shift controls continually compares
key shift parameters to pre-programmed ideal shift
conditions. The Allison Transmission
®constantly makes
adjustments to improve vehicle performance according
to the way the vehicle is being used, such as with a
heavy load. During this adaptive shift controls process,
some shifts may feel different as the transmission
determines optimum settings for a particular shift.
By using shift stabilization and adaptive shift controls,
the Allison Transmission
®shift schedule is variable and
adjusts to how the vehicle is being used, providing
improved vehicle performance.
2-28

Tow/Haul Mode
If your vehicle has an automatic transmission, it may be
equipped with a Tow/Haul mode. The selector button
is located on the end of the column shift lever. You can
use this feature to assist when towing or hauling a
heavy load. Turn Tow/Haul on and off by pressing the
button until the Tow/Haul indicator light illuminates
on the instrument panel.Tow/Haul is a feature on automatic transmission
equipped vehicles that assists when pulling a heavy
trailer or large or heavy load. Tow/Haul mode adjusts
the transmission’s shift pattern to reduce shift cycling,
providing increased performance, vehicle control,
and transmission cooling when towing or hauling
heavy loads.
If your vehicle is equipped with an Allison
®transmission,
you may have both Tow/Haul mode and overdrive
disable. See “Tow/Haul Mode” underTowing a Trailer
on page 4-69for more information.
Grade Braking
(Allison Transmission®Only)
Grade braking uses the engine and transmission to
slow a loaded vehicle on hills in addition to using the
brakes, saving on brake wear and increasing vehicle
stability. The Allison Transmission
®, when sensing
the driver’s desire to slow down while driving
downhill, will automatically shift to the next lower
gear range to assist in slowing down the vehicle.
2-30

Grade braking is active and automatic both in Tow/Haul
mode and normal shift mode. Grade braking is more
aggressive when in Tow/Haul mode and can
automatically downshift to SECOND (2), which is
different than grade braking while in normal shift mode
where automatic downshifts are limited to FOURTH (4).
The tachometer for both the diesel and gasoline
engine shows a dashed red zone and a solid red zone.
The dashed red zone indicates where a transmission
shift occurs for full engine power. When using grade
braking, the transmission’s shift point is adjusted to just
prior to the solid red zone, providing the bene t of
additional engine braking.
Grade braking driving within the dashed red zone is
normal, both the diesel and gasoline engine have been
designed for this grade braking feature. Do not allow
the engine to go into the solid red zone. Apply the
vehicle’s brakes for a short time to slow down if you are
driving on a long hill and the tachometer needle
enters the solid red zone. SeeTowing a Trailer on
page 4-69for more information.Overdrive Disable
(Allison®Transmission Only)
If your vehicle has an Allison Transmission®, you may
have the overdrive disable feature. The overdrive disable
feature prevents the transmission from shifting into
FIFTH (5) gear. The selector button is located on the
end of the column shift lever. You can turn overdrive
disable on and off by pressing and holding the button at
the end of the column shift lever until the indicator
light, on the instrument panel, illuminates.
If your vehicle has both Tow/Haul and overdrive disable,
tap the button once to enable or disable Tow/Haul,
and press and hold the button to enable or disable
overdrive disable.
2-31

Manual Transmission Operation
Five-Speed (VORTEC™ 6000 V8 Engine)
Here is how to operate
your transmission.
FIRST (1) is intended only for heavy loads or trailer
towing and is not recommended for normal driving.
During the rst 500 miles (805 km) of vehicle use, start
your vehicle moving in FIRST (1). This allows clutch
components to break-in properly.FIRST (1):Press the clutch pedal and shift into
FIRST (1). Then, slowly let up on the clutch pedal as
you press the accelerator pedal. Shift into FIRST (1)
only when the vehicle is below 5 mph (8 km/h). If you
try to shift down into FIRST (1) at excessive vehicle
speeds, the shift lever will not move into FIRST (1) until
vehicle speed is reduced.
SECOND (2):Press the clutch pedal and shift into
SECOND (2). Then, slowly let up on the clutch pedal as
you press the accelerator pedal.
You can shift into SECOND (2) when you are going less
than 20 mph (32 km/h). If you have come to a complete
stop and it is hard to shift into SECOND (2), put the
shift lever into NEUTRAL and let up on the clutch.
Press the clutch pedal back down. Then shift into
SECOND (2). If you try to downshift into SECOND (2) at
excessive vehicle speeds, the shift lever will not move
into the SECOND (2) position until the vehicle speed
is reduced.
THIRD (3):Press the clutch pedal and shift into
THIRD (3). Then, slowly let up on the clutch pedal as
you press the accelerator pedal.
2-32