A variety of twisting mountain roads and broad expanses of rolling multilane highways were
recently the test tracks on which we evaluated the brand-new Chevrolet and GMC Heavy-Duty
2500 and 3500 pickups. Our driving exercises included a fair amount of towing a 9,000-pound
travel trailer.
We came away with strong impressions of these new pickups, and although we
drove many trucks, most of our time was spent in a Duramax turbo-diesel-powered 2011 GMC
Sierra Denali HD 2500 pickup. For that reason, much of our report will focus on this
configuration.
Premium Tool
The Sierra Denali HD is GMC’s expression of capability blended with premium features and
styling. High styling for Denali interiors is expected, and we found nothing less when it
came to comfort and infotainment features, such as mobile Wi-Fi (available in all 2011
Chevrolet and GMC HD trucks), USB and Bluetooth connectivity, XM radio, OnStar 9.0 and
navigation. Seating is plush, but firm and supportive. All the vehicle performance and
operation gauges, dials and controls are easy to read and to reach, although I found the
center-mounted HVAC system’s tiny buttons and switches too small and not easy to see or
use.
Exterior styling hasn’t been radically altered; the new truck looks much like the 2010
model. A four-bar chrome grille with round air inlets sets the Denali apart from other GMC
trucks, along with body-match bumpers and the buyer’s choice of 17-, 18- or 20-inch wheels.
However, it’s under the skin that the truck’s true nature is revealed.
Action-Ready
Highlights
The 360-hp Vortec 6.0-liter V-8 gas engine and six-speed automatic transmission powertrain
combo (also both revamped for 2011 to deliver more power and better drivability) is
standard on all HD pickups. However, when a properly equipped 3500 is ordered with the new
Duramax 6.6-liter turbodiesel, the GM HD truck becomes the segment leader in power.
It’s
also the segment leader in towing capability, offering 17,000 pounds conventional and
21,700 pounds fifth-wheel towing capacity. The Duramax 6.6-liter V-8 turbodiesel has seen
some enhancements for 2011, as has the Allison 1000 transmission. And the new truck offers
a smorgasbord of control features, such as a new “smart” exhaust brake, integrated
trailer-brake controller, and hill-start assist – to name just a few – that help make
towing big loads a lot less stressful.
Support Structure
The frame has been completely redesigned and features all-new, fully boxed frame
assemblies. It offers increased cross sections and uses more high-strength steel, and the
front section is hydroformed. The new, larger engine and transmission mounts, coupled with
the much stiffer front frame section, provide greater vibration damping, while the
hydraulic body mounts that are underneath the cab of the truck on extended and crew cab
models help deliver a more isolated and comfortable ride inside for passengers.
In
addition, access holes in the rear frame section allow easier installation of
fifth-wheel/gooseneck-style hitches. The frame-mounted hitch for conventional trailer
towing features a stronger box-tube design, helping support a conventional tow rating of up
to 17,000 pounds (again, with a properly equipped 3500).
A completely redesigned
independent front suspension offers a front axle weight rating of up to 6,000 pounds,
depending on the specific model, but the signature short-long arm/torsion bar front
suspension design was retained. However, now it features new forged-steel upper control
arms that are stronger and lighter, and new precision-machined cast-iron lower control arms
for handling greater loads. It also now uses a pair of urethane jounce bumpers on each
side, instead of just one, for improved load handling. There’s also a new, stronger upper
shock mount design.
The new rear end features a larger asymmetrical leaf-spring design that
helps to improve ride and handling. This also helps enhance traction control system
efficiency, and minimize rear-axle wind-up, which can cause axle hopping. The 2500 HD
models offer two-stage leaf springs; 3500 HD trucks feature three-stage springs. All models
have 3-inch wide leaf springs that are 20-percent wider and help support the increased
gross axle weight ratings.
These improvements to the frame and suspension lead to positive
impressions on the road, as the trucks exhibit a smooth, crisp road experience in general,
with no wallowing or sloppiness present during any driving maneuvers.
A longer wheelbase
and wider tracks front and rear probably have something to do with that. New shocks
specially tuned to match the truck’s weight don’t hurt either. And a revised steering
system that includes a larger steering gear, new linkage and a more powerful steering pump,
no doubt, helps out as well.
Brake System
A four-wheel, four-channel ABS is standard on all single-rear-wheel models and a
three-channel is standard on dual-rear-wheel models. The revised hydroboost system has
reduced pedal effort and pedal travel, which was noticeable in the cab, and the truck
stopped straight and true in non-towing as well as in towing situations. The huge (14-inch)
rotors on all four wheels are complemented by larger wheel hub and bearing assemblies, and
the rear rotors attach to the hubs for easier servicing.
An innovative “smart” exhaust
brake as a standard feature on Duramax-equipped models supports these big brakes. The
driver can select to use the turbine control of the variable geometry turbocharger and the
compression of the engine to generate backpressure to slow the truck when towing a trailer
down a hill without having to use excessive service brakes. It’s integrated into the cruise
control, and can take into account the grade and vehicle load. The driver can turn on the
exhaust brake feature, turn on cruise control, set the speed desired, and then let the
truck do the driving with the trailer in tow.
When the exhaust brake is used in “manual”
mode (engaged without the cruise control on), the transmission and the exhaust brake work
together to offer the driver the ultimate in braking control and assist in maintaining the
desired vehicle and trailer speed down a hill. Used in either mode, the exhaust brake
worked well during our evaluation and had a dramatic effect on controlling the vehicle and
its towed load.
Safety First
The 2011 GM HD trucks feature a full lineup of safety features including Stabilitrak
electronic stability control (on all single-rear-wheel models), but our two new favorites
for towing are Trailer Sway Control system (single-rear-wheel models only) and Hill Start
Assist.
The trailer-sway system kicks in when it senses excessive yaw in the tow vehicle
and intervenes by applying the brakes and/or reducing engine power to bring the trailer
back under control and keep it going in a straight path. The system integrates with
electric trailer brakes when a trailer with electric brakes is plugged into the truck’s
wiring harness.
Its hill-start system is automatically engaged when the vehicle senses that
it has stopped on a grade of about 5 percent or greater, then it holds the brakes for about
1.5 seconds or until the gas pedal is depressed, preventing the vehicle and trailer from
rolling backward.
Power Partners
For 2011, the potent Duramax offered in the GMC HD 2500 Denali has been made even more
powerful with a few enhancements. The aluminum heads, common-rail fuel injection and
six-bolt-per-cylinder design is the foundation of the sturdy turbodiesel powerplant, but a
few internal elements help build power and create better efficiency and durability. Among
these are an EGR cooler bypass to reduce high-mileage soot deposits in the cooler and EGR
circuit, a new higher strength piston design to eliminate bushings and lower reciprocating
weight, modified connecting-rod pin ends to increase piston support, a change in the
turbo’s oil circuit to increase pressure for faster oil delivery and increased oil-pump
flow for more pressure at low speeds. In addition, a new 30,000-psi piezo-actuated
fuel-injection system, that’s also capable of using ASTM grade B20 biodiesel, ensures a
more precise delivery of fuel and lowers emissions.
The Allison 1000 transmission has also
had its fair share of enhancements or carryover features for 2011, including greater torque
handling capability, improved lock-up operation, cruise-grade braking, tow-haul mode and
driver shift control with tap-up/tap-down range selection.
A gentle tap-down on the
transmission’s driver shift control (DSC) allows the operator to manually select and hold a
desired gear, and it inhibits downshifts when the engine speed is above allowable rpm
limits. The Tow/Haul mode is driver-selectable as well, and provides greater control during
towing situations – when engaged, the shift schedules are altered so the torque converter
locks up earlier and takes better advantage of engine braking when towing downhill.
To meet
the increased power output of the new Duramax, the Allison was also upgraded with
structural improvements that include increased strength for the input and main housings, a
new higher-capacity torque converter and increased clutch and shaft torque capabilities. A
new 4WD output housing is also matched with the upgraded transfer case for 2011 models.
During our time behind the wheel of the 2011 GMC Sierra Denali, the Duramax/Allison
powertrain pair performed flawlessly, muscling the trailer up mountains and keeping it
under control down steep inclines without breaking a sweat or losing its composure. Power
came up fast, with little or no turbo lag, and the engine’s power band was broad enough and
the transmission was so adaptable with its many modes of operation that it was easy to stay
within quick reach of acceleration.
There are dozens of models in the new lineup, but in
our opinion, the ultra stylish and powerful GMC Sierra HD Denali leads the redesigned
roster of 2011 GMC and Chevy trucks. Offered for the first time in the upscale Denali
package, the Sierra sets a new standard with its blend of style, performance and premium
features.
General Motors Corporation, (800) 551-4123, www.gmc.com.
