APACHE JUNCTION, Ariz. -- Four black on/off-road Bridgestones on a four-wheel-drive version of Chevrolet's full-size Avalanche sport utility plow through sand as a smart transfer case channels big-time engine torque between front and rear wheels to maintain traction while we inch along Arizona's treacherous Apache Trail, a narrow trace carved into red-rock canyon walls with twisty switchbacks framed against sheer cliffs.
One driver's brain protests this dicey traverse of a desert canyon where too much wheel slip could send this 5645-pound chunk of machinery hurling through thin air to the bed of the Salt River far below.
Yet we don't sweat the drive because our vehicle packs serious mechanical hardware and sophisticated safety systems to transport us securely along the Apache Trail -- and in surprising comfort.
The 2010 iteration of Chevrolet's Avalanche is a big-rig vehicle stoked with a powerful engine and -- despite a bulk of nearly three tons -- capable of surprisingly nimble maneuvers.
It's also unusual in configuration, as there's the abbreviated bed of a pickup aboard plus the big cabin of a super-size sport-utility wagon with four full-size doors and two rows of comfortable seats for passengers.
The jumbled configuration makes Avalanche a multi-purpose machine which functions as both a wagon and truck, thus explaining its descriptive tag of sport utility truck, or SUT.
Chevrolet rolled out the original Avalanche as a 2002 model derived from Chevy's super-size Suburban SUV yet discarding Suburban's boxy rear bay in favor of the shortened bed of a pickup truck.
Our test vehicle tracking through Arizona canyons is based on the GMT-900 platform of General Motors which also supports GM's big SUVs -- Chevrolet Suburban and Tahoe, GMC's Yukon and the Cadillac Escalade.
The GMT-900 platform has boxed frame rails stretching from tip to tail to forge a firm foundation.
Also, there's a wide track for front and rear wheels and a low center of gravity for the overriding structure, which makes Avalanche quite stable in motion and, when coupled to a tuned suspension, enhances the ride quality and the vehicle's ability to move through a set of curves without much body roll.
The suspension is a coil-over-shock arrangement up front and a five-link design at the rear with coil springs.
An optional Autoride rear suspension device employs continuously-variable road-sensing damping with air-leveling shock absorbers for precise control over bumps.
The steering system is a rack and pinion mechanism, not that common among truck-based SUVs. It brings quick and predictable response from the steering wheel.
Brakes consist of big disc on every wheel, with linkage to a computerized anti-lock brake system (ABS), traction control system (TCS) and GM's StabiliTrak anti-skid yaw controller.
Actually, we're surprised by the agility and easy-driving nature of this Avalanche -- it doesn't behave like a gigantic truck that occupies more than 18 feet of real estate from nose to tail.
The V8 displaces 5.3 liters and comes with GM's Active Fuel Management (AFM) technology which cuts by half the number of cylinders engaged in the combustion process when boosted power is not needed in order to conserve fuel.
Big engines generally denote a dog-thirsty appetite for lapping up fuel, but the AFM device is a real fuel-saver and turns Avalanche into a rather efficient vehicle.
The plant generates big muscle -- 310 hp at 5200 rpm and 335 lb-ft of torque at 4400 rpm when sipping gasoline, or 326 hp at 5300 rpm plus 350 lb-ft of torque at 4400 rpm with E85 in the tank.
Federal EPA fuel economy scores for Avalanche tally to 14 mpg city and 20 mpg highway for gasoline or 10 mpg city and 15 mpg highway with E85.
Styling for Avalanche's external package employs clean lines which seem to diminish the scale. Up front the SUT wears a fat-lip fascia fitted with square-hole foglamps and faux skid plates, a twin-port horizontal grille with narrow chrome mesh insert, and squarish headlamp clusters.
There's a keen rake to the windshield and a bulging power dome on the hood, squared wheelwells on flanks with subtle fender flares but smooth sides on the doors, save for a single strip of protective molding.
Avalanche 2010 offers trim designations of the entry-level LS, a well-equipped LT and top-tier LTZ, each with a choice of rear-wheel two-wheel-drive (2WD) or four-wheel-drive (4WD) traction.
All trim versions retain a feature from the original edition which sets Avalanche apart from other vehicles: The back wall of the cabin also works as a door. It folds down flat after the back seat tumbles forward and forms a generous extension of the truck box, which grows from 63.3 to 98.2 inches.
This back gate -- called a Midgate -- consists of three parts that include a window at the top, a mid-level brace and the composite lower panel.
You can drop the panel, leaving glass and brace in place and creating a horizontal portal to accommodate long and thin loads like tubular poles, lumber or 4x8 sheets of plywood. A three-piece rigid cargo cover tops the truck box and seals bed and contents from weather.
You may also detach the window and stow it in a special slot on the panel, then fold the panel with attached brace to completely open the rear space. That enables Avalanche to carry bulky items, such as a stack of sacks filled with building material like mortar, or a portable generator, a coupe of dirt bikes, even a big snowmobile or aqua scooter.
Or you could leave the Midgate locked in place but the rear seatback folded down to make a water-tight compartment stuffed with fragile goods while the truck bed in back carries other wares not sensitive to the weather.
Safety equipment aboard Avalanche ranges from frontal air bags for front seats and curtain-style air bags for both rows to three-point safety belts for all seats and a tire pressure monitoring system (TPMS).
Chevrolet sets price points for the 2010 Avalanche at $35,720 for the LT 2WD and $38,775 for LT 4WD.