Ride quality is excellent, the best among the duallies currently available from Ford and Dodge. Handling is surprisingly good for such a big truck. It covers real estate quickly, whether on the Interstate or on winding back roads. A hydroformed front frame gives it extraordinary rigidity, which allowed GM's engineers to tune the suspension more precisely for a better ride and handling. Front suspensions use torsion bars for durability.

Four-wheel disc brakes have reduced stopping distances and give the driver a solid pedal feel, a huge improvement over GM's previous-generation trucks. Bigger front rotors, larger brake pads, improved linings offer better stopping power and longer pad life. Dynamic rear proportioning shortens stopping distances by transferring front and rear brake bias to the tires with the best grip.

The base engine is the Vortec 6000, a 6.0-liter V8 (366 cubic inches) that generates 300 horsepower and 360 foot-pounds of torque at 4000 rpm. Introduced for 1999, it's designed for a 200,000-mile operating life with 10,000-mile oil change intervals. Its aluminum cylinder head is similar to that of the L56 Corvette. It comes with a choice of a heavy-duty five-speed manual and GM's 4L80-E four-speed electronically controlled automatic, which comes standard on Extended Cab and Crew Cab models. The four-speed automatic features a Tow/Haul mode.

The big Vortec 8100 V8 delivers 455 pounds-feet of peak torque at 3200 rpm. Torque is that force that propels the truck off the line and this 8.1-liter, 496 cubic-inch V8 has gobs of it. It generates 400 lbs.-ft. at just 1600 rpm. Don't expect neck-snapping acceleration, however. Quicker acceleration performance when towing is the objective. And it does this very well. Introduced last year, this 8.1-liter V8 replaces GM's 7.4-liter V8. It has advanced features such as an engine oil life monitor and a limp-home mode. This gas engine is an $850 option.

The new Duramax 6600 diesel is smooth, quiet, and powerful. It punches out an amazing 520 lbs.-ft. of torque at just 1800 rpm. GM's Duramax diesel engine is built in Moraine, Ohio, but was developed with Isuzu, one of the world's largest manufacturers of diesel engines. The new 6.6-liter Duramax offers improved fuel economy over the old 6.5-liter GM diesel it replaced. The Duramax was designed for a 200,000-mile operating life, according to GM engineers, and for easy serviceability. Half of heavy-duty truck pickups are sold with diesel engines. The diesel adds $4810.

The Duramax and Vortec 8100 offer a choice of a ZF six-speed manual or optional Allison 1000 five-speed automatic ($1200). Both have close-ratio gearing, which provides exceptional launch, hill climbing, and towing capability and economy. Their heavy-duty components are stronger than those typically found in one-ton truck transmissions, providing exceptional durability.

The ZF six-speed manual is easy to shift and is fully synchronized in all gears with dual-cone synchronizers in second and third. A convenient shift pattern allows the shift lever to be moved forward for reverse and straight back for first, making it easier to maneuver quickly in tight spaces. Second gear works well for taking off with a light load; first is a creeper gear.

As good as the six-speed manual is, the optional Allison five-speed automatic is one of the most impressive features of these trucks. We highly recommend it for its responsive performance. Available for the Vortec 8100 and Duramax engines, the Allison is designed to last 200,000 miles; GM engineers said it's "over-designed," meaning it's heavier duty than it needs to be. But it's also sophisticated and keeps in close contact with the driver and the engine with full electronic control. It adjusts shifting according to driving style. The Tow/Haul mode keeps the transmission in gear longer to reduce hunting and heat buildup. This transmission senses when the truck is going downhill, senses when the driver is applying the brakes and downshifts, reducing wear on the brakes. This grade braking feature works great; just touch the brake pedal as the truck is going down a grade. On a practical side, the Allison transmission is set up to make it easier to attach power take-off (PTO) accessories. It downshifts crisply as the truck comes a stop. The Duramax and Allison combination does not come cheap, however.

GM says its heavy-duty pickups offer the highest GVWR for hauling and the highest GCVW for towing in the business. Payloads range from 3321 pounds for a 2500HD Crew Cab 4WD to 5753 pounds for a 3500 Regular Cab 2WD. Two-wheel-drive models and smaller cabs offer higher payloads. The heavy-duty trailering option adds an adapter that permits four-way and seven-way trailer-harness connections.

Both the Vortec 8100 gas and Duramax 6600 diesel permit towing trailers up to 12,000 pounds. We pulled a 7000-pound trailer (a two-horse tandem-axle trailer full of bags of shot) in a 2500HD with the Duramax diesel and Allison transmission. Attached via a (Reese) Class III load-distributing hitch, it was a stable rig, easy to manage. With a fifth wheel setup, trailering capability increases to an astounding 15,800-pound maximum.

4WD trucks get a shift on the fly transfer case. Using the floor-mounted shifter, it shifted immediately into 4WD at 40 mph.

"Heavy duty" is a good descriptor for the 2500HD and 3500 trucks as all of their hardware is beefier than what is found on the 1500 and 2500 light-duty pickups. Front tow hooks are standard.