Called the Vortec 4200, the 4.2-liter inline-6 features dual overhead camshafts, four valves per cylinder, and variable phasing of the exhaust cam. It's rated 275 horsepower and 275 pound-feet of torque. (Torque is that force that thrusts you off the line and up steep hills.) Ninety percent of the peak torque is available at just 1600 rpm and it's still there at 5600 rpm. The engine is still striding, not screaming, when the full-throttle upshift comes at 6000 rpm. That torque gave us confident power when attempting passes on steep uphill two-lanes. It offers strong acceleration without forcing the transmission to downshift. The four-speed automatic transmission is programmed well and makes a good companion for the engine. Shifts are smooth.

Towing was a high priority in the TrailBlazer's engineering. Six-cylinder models are rated to tow 6300 pounds with 2WD, 6100 with 4WD. The six-cylinder engine is designed to run cool while towing, thanks in part to a big seven-quart oil pan.

Big ventilated disc brakes provide stopping power, and four-wheel ABS is standard. Under hard braking, the nose didn't dive, keeping the TrailBlazer remarkably level and stable.

We found the ride excellent, very smooth without being too soft. The TrailBlazer was designed to lean up to 5 degrees in corners, and then stop leaning. It features a wide track and low engine position, which drops the center of gravity. A vehicle with a low center of gravity is generally less likely to roll over than a vehicle with a high center of gravity. TrailBlazer has a very tight turning circle of 36.4 feet, because the suspension and engine design allow for large steering angles.

The chassis and suspension are highly developed with design features normally associated with sports cars: rack-and-pinion steering, four-wheel vented disc brakes with twin-piston calipers in front, independent front suspension with short/long control arms, live rear axle using five-link location with Bilstein gas-charged shock absorbers and coil springs, and thick antiroll bars front and rear. TrailBlazer's chief designer had previously worked on the Camaro and Firebird and his approach was to put some "sport" in this sport utility. The chassis rails are shaped by hydroforming, which makes them stronger and lighter. No less than eight crossmembers contribute to TrailBlazer's torsional rigidity, and there are 12 tuned body mounts that use rubber pads and hydrualics to dampen vibrations.

Leaving the highway for the dirt, we found the TrailBlazer impressively stable on washboard surfaces. It bottomed on dips, however, signaling that the optional skid plates ($130) are necessary for off-road driving. When equipped with the 17-inch on/off-road tires and skid plates, the TrailBlazer easily chugged along at 5 mph through soft sand in Auto4WD.

Four-wheel-drive TrailBlazers feature GM's Autotrac system, which offers four settings: 2WD, Auto4WD, 4HI and 4LO. Switching in and out of 4WD can be done on the fly with a flip of a switch. The transmission must be in neutral to engage or disengage 4LO. In Auto4WD, power is shifted to all four wheels as conditions require. The TrailBlazer can be towed in the Auto mode without having to disconnect the driveshaft, a convenient feature. Traction control ($195) is available for 2WD TrailBlazers.

As impressed as we were with the TrailBlazer, we were less than enchanted by the TrailBlazer EXT. The long-wheelbase EXT lacks the responsiveness and stable handling of the standard TrailBlazer. The EXT feels long and narrow. That's not surprising, given that the TrailBlazer EXT is longer, narrower and taller than a Tahoe. TrailBlazer EXT's wheelbase is stretched dramatically, by 16 inches. Its suspension is soft. It wallows in corners. On exit ramps, when braking and turning at the same time, it does not feel as crisp and stable as a TrailBlazer or Tahoe. On the highway, the EXT wanders around in the lane. Stability is also affected by strong crosswinds at high speeds. Plus it's heavier. A V8-powered TrailBlazer EXT weighs at least 400 pounds more than a standard TrailBlazer. Even equipped with the optional V8 engine, the TrailBlazer EXT feels distinctly underpowered.

The V8 features some interesting technology that improves fuel efficiency. A V8 of the same size was offered last year, but the 2005 engine is all new and features Displacement on Demand (DOD), which shuts down four of the eight cylinders when they are not needed, for up to 8 percent better fuel mileage under light-load conditions. The engine-management computer instantly revives the sleeping cylinders the second the driver demands more go. With this system, even the 5000-pound 4WD EXT can squeeze 15/18 city/highway mpg. We drove one that GM engineers had rigged up so that they could detect when the pistons were being activated and deactivated, but we could not feel it through the seat of our pants. It all happens seamlessly. This new V8 produces slightly more horsepower and torque than the engine it replaces.