CUSTER, S. D. -- Hugging blacktop on a rambunctious route threading around towering granite ramparts in the Black Hills of South Dakota, we're cruising the American West in a luxurious new sport utility vehicle of super-size scale.
Stretching more than 18 feet long from the front bumper to the tail door and tipping scales to a figure approaching three tons, the GMC Yukon XL -- that's XL, as in "Extra Large" -- happens to be one of the largest SUV on our planet, save for the GM sister ships like Suburban by Chevrolet or Escalade ESV by Cadillac.
It's a grand wagon which measures even larger than the full-size Yukon SUV.
Overall length of the XL edition exceeds Yukon by 20.4 inches, in fact, and there's about 14 inches of extra space applied lengthwise at the rear of the cavernous cabin which contributes more legroom for riders on third-row seats and three times the cargo space (at 45.8 cubic feet) behind the third seats.
Our tester Yukon XL in half-ton 1500 series dresses up in deluxe Denali trim.
Denali -- a name drawn from native Alaska Athabascan people to describe "the High One" of Mt. McKinley, tallest peak on the North America continent -- is the pinnacle edition of super-size Yukon XL in a leather-lined issue charged with class-capping horsepower.
The Denali designation first appeared in 1998 on a tricked-up version of Yukon, but this new one for 2010 stands out with a sophisticated monochromatic color scheme in new tints like Dark Labyrinth Metallic or Sheer Silver Metallic spread over the boxy rectangular format.
It's accented by a powerful face with a clean mesh grille wrapped in chrome and flanked by sparkling lenses of vast corner headlamps studded with bright halogen bulbs.
Flanks show smooth lines on doors except for a single strip of protective molding which introduces curvy forms to interrupt the boxy package.
Yukon XL Denali configures with rear-wheel two-wheel-drive (2WD) or four-wheel-drive (4WD) traction.
Our tester Yukon XL Denali for the Dakota Black Hills carries the 4WD mechanism which employs GM's automatic Autotrac system with a smart electronic transfer case delivering on-demand all-wheel-drive (AWD) traction.
And packed aboard that boxy structure you'll find every conceivable mechanical weapon for serious road combat, along with every convenience in a leather-wrapped cabin that cradles up to seven riders in the lap of luxury.
But our surprise is that this humongous sport utility behaves like a souped-up sprinter.
Stomp the throttle but prepare yourself for a neck-snap launch because the big wagon is charged with fire power.
Below the square-cornered hood there lurks an aluminum-block V8 engine which displaces 6.2 liters and applies variable valve timing (VVT) to optimize camshaft timing and enrich the low-rpm torque and high-rpm horsepower
The plant produces 403 hp at 5700 rpm and torque of 417 lb-ft at 4300 rpm.
All of that muscle is translated through a six-speed automatic gearbox with clutch-to-clutch shifting and a wide overall ratio.
Only a handful of sporty performance cars pull so much power out of a V8 -- but how about a leather-lined and super-size SUV?
For 2010 Denali issues the 6.2-liter V8 gains GM's Active Fuel Management (AFM) technology which cuts by half the number of cylinders engaged in the combustion process in order to conserve fuel when boosted power is not needed.
Big engines generally denote a dog-thirsty appetite for lapping up fuel, but the AFM device works as a fuel-saver and turns the big XL Denali engine into a rather efficient vehicle.
Federal EPA fuel-burn numbers for Yukon XL Denali climb to 19 miles per gallon for highway travel with 2WD traction, or 18 miles per gallon with the 4WD version.
Despite the best-in-class fuel economy, the V8 also earns high scores for towing a trailer, capping at a 7900-pound tow capacity for the 2WD version.
Yukon XL rides on GM's GMT-900 platform which 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 the SUV 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.
Standard for XL Denali edition is GM's Z55 suspension package with the Autoride continuously-variable road-sensing damping up front and rear load-leveling shock absorbers for precise control over bumps.
The steering system is a rack and pinion mechanism, not particularly common on truck-based SUVs. Using a 17.75:1 steering ratio, it brings quick and predictable response from the steering wheel.
Brakes consist of a big disc on each wheel, with linkage to a computerized anti-lock brake system (ABS), traction control system (TCS) and GM's StabiliTrak anti-skid yaw controller.
The leather-wrapped passenger compartment in the Yukon XL Denali contains three tiers of seats for as many as seven riders.
There's a pair of broad buckets on the front row, a second row in fold-and-tumble buckets or split bench plus a pair of seats on the third row which fold and may be pulled out individually like a rollaboard suitcase to maximize cargo space.
At the back of the cargo bay, a power-assisted liftgate opens and closes with the tap of a finger button.
Safety equipment aboard ranges from frontal air bags for front seats to three-point safety belts for all seats and a tire pressure monitoring system (TPMS), with curtain-style air bags for all three rows and new side thorax air bags added at the front seats.
The MSRP for GMC's 2010 Yukon XL Denali starts at $55,670 for a 2WD edition.