CAREFREE, AZ – “Fuel economy is a game of inches,” says a General Motors Corp. engineer in describing the new Chevrolet Silverado’s fuel economy at a media event here.

Even a relatively small change, including a new module that helps lower the engine’s internal pressure during idle, shaves 0.2 mpg (1,176L), he says. But taken as a whole, innovations on the new Silverado and GMC Sierra fullsize pickups gain 6.5% in overall fuel economy.

The same principals applied in building GM’s new pickup trucks, officials say. The battle is won or lost in the details, those tiny improvements that add up to make a next-generation vehicle better than both its predecessor and benchmarked rivals.

With this in mind, GM leaves little to chance with its new fullsize trucks. Engineers and executives, alike, seemed to have anticipated every possible gripe before critics had a chance to level them. The implied company mantra is: “Anything Toyota and Nissan can do, GM can do better.”

Yet, in many ways, the ’07 Chevrolet Silverado and GMC Sierra have much in common with the Japanese brands, which are known for their rabid pursuit of perfection. This applies even to subtle engineering advancements.

When opening a rear door on a Sierra extended cab, which swings to a 170-degree angle, Gary White, vehicle line executive fullsize trucks, notes: “That’s two degrees more than the Nissan Titan.”

Considering the importance of the light- and heavy-duty Silverado and Sierra, which, together, currently represent one of every 10 vehicles GM sells worldwide, such incremental gains are important.

However, the major step forward is the new GMT900 platform, an architecture that likely saved the ’07 Chevy Tahoe and GMC Yukon from SUV oblivion during the summer’s skyrocketing pump prices.

The new platform is a true evolutionary step forward from the GMT800, on which shifting chassis weight can be felt even on the newest of Arizona highway pavement. The GMT900 all but eliminates this problem, delivering a far more sturdy drive compared with the GMT800.

The new platform creates wider front and rear tracks by 3 ins. (7.6 cm) and 1 ins. (2.5 cm), respectively. And the regular cab/standard box Silverado/Sierra is about 3 ins. longer, 1.4 ins. (3.5 cm) wider and 2.7 ins. (6.8 cm) taller than the previous generation, all while maintaining the same wheelbase.

The trucks boast a whopping 234% boost in torsional stiffness, which is aided by hydroformed siderails on the front frame, a first for the truck platform.

That’s combined with a new Eaton Corp. automatic-locking rear differential that increases traction on demand, plus a new rear suspension with splayed shock absorbers, coil-over-shock front suspension and rack-and-pinion steering.

The myriad enhancements are apparent during a rocky-road test drive here. The new trucks absorb the shock of glancing boulders and road dips with tolerable jostling of the occupants. With the GMT900’s closed-boxed frame, compared with the GMT800’s open C-section, the cab and bed ride as one unit.

A choice of five suspensions, catering to the off-road contingent and trailer-towing crowd, are available options. The new duo models lead the segment in towing, maxing out at 10,500 lbs. (4,763 kg) with payload limits reaching 2,160 lbs. (980 kg).

In a closed course at GM’s Mesa proving grounds here, the 6L Silverado LT gives little pushback while hauling the maximum weight, compared with its Nissan Titan competitor that pulls an 8,500-lb. (3,856-kg) trailer with less than confident braking.

Design-wise, GM mostly plays it safe, opting to hone the new, instead of throwing out the old. The Silverado nixes its cat-eyed headlights, choosing instead boxy headlamps and prominent fog lamps. The front and rear fenders offer more curve, which accents a higher beltline.

The Sierra has a more angular side look to its head lamps, but subdues its front fascia by getting rid of the slightly concave front bumper in favor of one that is straight-edge chrome.

Inside, GM introduces new premium and “pure pickup” interiors.

The Silverado WT and LT and Sierra WT and SLE trims sport the pure pickup interior, including larger control knobs and interior door handles that are ergonomically designed for glove-wearing drivers and passengers.

The instrument panel adds a new “double” glove box that melds a conventional lower compartment with a covered storage hatch above.

Among other storage perks, a new, 40/20/40-split front bench houses a fold-down console with integrated cupholders and 0.22 cu.-ft. (6.1L) of space. A locking under-seat bin provides 0.32 cu.-ft. (9.1L) of space and a 12-volt power outlet for the computer-carrying contractor.

Extended cab and crew-cab models feature new stadium-style rear seats that easily are folded forward, freeing up floor room across the rear section of the cab. A power-slide rear window also is available.

The new “low and forward” instrument panels are 5 ins. (12.7 cm) lower in the luxury interiors and 3.5 ins. (9 cm) lower in the pure pickup interiors. They are expected to spread across several GM vehicle lines.

Premium interiors are standard on the Chevy Silverado LTZ, GMC Sierra SLT and upcoming Sierra Denali. Strategic wood-grain and brushed chrome trim accents, heated leather bucket seats and a leather-covered steering wheel add to the lux-truck feel.

Active fuel management, GM’s version of cylinder deactivation, is standard on the fourth-generation 5.3L and 6.0L V-8 engines, which the auto maker reckons will be the most popular of the eight powertrain configurations offered.

Environmental Protection Agency ratings for the 5.3L are 16/22 mpg (14.7 and 10.7L/100 km) in city/highway driving, respectively, for 2-wheel-drive models. The 6.0L is rated at 15/19 mpg (15.7L-12.3L/100 km), respectively, for both 2WD and 4-wheel-drive trucks.

GM eliminates manual transmissions on the trucks in favor of a 4-speed automatic for now. The Sierra Denali will be the first to receive a new 6-speed gearbox when it premieres in March. The other trims will have to wait until 2008 and 2009 for the 6-speeds.

Prices on ’07 extended- and crew-cab versions will hold steady with ’06 vehicles. The extended-cab models start at $23,605 and crew cabs base at $27,000, unchanged from the current price.

The 2WD regular cab starts at $18,760, while the 4WD regular cabs stickers at $21,860, marking a $2,045 and $1,715 increase, respectively, from ’06 model pricing. All prices include a $900 destination charge.

GM pushed the envelope not only in the execution of its new trucks but also on the timing of their rollout. Moving their sales launch up 13 weeks gives the auto maker a much-needed tailwind.

Meanwhile, Toyota’s 1-month delay in launching sales of its all-new Tundra delights a confident White.

“We want (Toyota) to dump a bunch of resources into doing their trucks at the expense of their cars,” he tells Ward’s. “Look at all the product delays they have now.”

Consider those fighting words in GM’s defense of the last major vehicle segment not fully infiltrated by Japanese auto makers. The battle heats up in February, when the Tundra comes to town.

scanderson@wardsauto.com