It was 24 short months ago when GM pulled the GMT900's production schedule forward almost six months for a January 1, 2006 on-sale date. Most companies delay introductions due to unforeseen plant problems or technical difficulties; the reverse is often risky. Beyond showing confidence in the team that put these trucks together, it reveals that GM is pinning hope on the new platform that spawns the Tahoe and Suburban, along with GMC and Cadillac variants. Can a single SUV architecture save a company's profits at a time when its most viable segment is shrinking?

A first-drive smack-down test on the track and in the field reveals that GM brought game.

The old Tahoe was about as aerodynamic as a brick, so major work went into this area. There's a noticeable change in proportions: The windshield glass has more slope, the front end is reshaped, and the grille and bumper now work as a single aero-designed unit with few panel gaps. Likewise, changing the rear-end aero, smoothing out the mirrors, and lowering the airdam improved the overall drag of the full-size SUV by almost 12 percent--that means increased fuel economy. But fuel ratings have been bettered in other important ways, too.

GM is touting its Gen-IV 5.3-liter V-8 small-block as the most fuel-efficient engine in its class, with unadjusted combined-average fuel-economy ratings in two- and four-wheel drive above 20 mpg, due in large part to Displacement On Demand, the high-tech cylinder shutoff system. Move your foot on and off the throttle and watch the information display center, which indicates V-4 or V-8 mode. In addition to DOD, the new 5.3-liter engines (an all-aluminum version for 2WD models and a cast-iron block version for 4WD models, able to run E85 fuel) give the Tahoe more horsepower than any other vehicle in its class. However, both have less torque compared with Ford's 24-valve Expedition and Nissan's 32-valve Armada.

Look for the 4.8-liter GM small-block V-8 to become an option midyear 2006, with the possibility of a Tahoe SS version using the 400-horse, 6.2-liter V-8 that'll also power the new Escalade.