The GMC Sierra 2500 diesel isn't the biggest truck in the world, but it feels like it could pull the world.

Serious trailering jockeys draw a line in the sand when it comes to their brand preference: Ram HD, Ford F-series Super Duty or General Motors' Chevy Silverado HD and GMC Sierra HD.

Each of these beasts of burden is neck and neck for power ratings, and when one truck moves ahead one year, the others find more ponies the next.

The GM heavy-duty pickups have had some notable power improvements for 2011 and other refinements. And there is a new Denali top-line model with such features as brushed aluminum trim, power-adjustable pedals, a Bose surround audio system and 12-way power seats.

Exterior treatments include a four-bar, chrome grille (versus three bars in the half-ton pickups), more body-side chrome, body-color bumpers, and 18- and 20-inch polished forged aluminum wheels or 17-inch on the dually.

The Sierra Denali test truck had a starting price of $47,445 and was $61,774 as tested. The highlight of the package was the Duramax 6.6-liter V-8 turbo diesel ($7,195) and the Allison 6-speed automatic transmission ($1,200). Other useful travelers' options included the touch-screen navigation system with CD-audio upgrade and XM Nav Traffic, $2,250; heated and cooled front seats, $650; heated steering wheel, $150; and rearview camera, $450. For hitching trailers, the rearview camera is priceless — no more bellowing at a helper guiding the driver. Also available are Wi-Fi, USB and Bluetooth connectivity.

The list of features sounds luxurious, but these trucks are built first for work and the play-time accommodations are layered over the brawn. So even though your truck can be a wireless hot spot, it also has working-class plastic, traditional faux wood trim and work-boot durability. And paint colors are limited to Black, Stealth Gray and White.

The Sierra's cab is comfortable for the long haul, and it's so well sound isolated that it creates a bubble of calm for the driver who looks down upon the rushing world around. At 20 feet in length, parking places are like diesel stations: when you find one, you keep going back.

The backbone of the GMC HD is its heavy-duty, boxed frame, which now has more cross sections and more high-strength steel for rigidity and reduced vibration. Access holes to the rear frame section make it easier to install fifth-wheel/gooseneck-style hitches. And for conventional towing, the frame-mounted hitch has a box-tube design that's good for 17,000 pounds. Compared to the standard, half-ton Sierra, the HD's 4-wheel disc brakes — 13.97 inches front and 14.17 inches rear — are an inch bigger up front and 2.5 inches larger at the rear.

The standard powertrain is a 360-hp, 6.0-liter V-8 that produces 380 foot-pounds of torque at 4,200 rpm on regular unleaded. But when the driver is hauling a family and a mega travel trailer, the added power and driving range of the diesel-engine option may justify the cost.

The Duramax diesel, with exhaust brake, puts out 397-hp and 765 foot-pounds of torque at 1,600 rpm. Nitrogen-oxide emissions were cut by at least 63 percent over 2010 models. And it can run on B20 biodiesel.

Hit the gas and the turbo whistles up power quickly, and all that torque launches to the rear wheels in an impressive display of force. The Allison transmission includes tow-haul mode, which raises shift points to save on the transmission "seeking" the right gear, and an exhaust brake to use engine braking downhill and preserve the brakes.

Heavy-duty trucks have gross vehicle weight ratings of more than 10,000 pounds and are not subject to EPA fuel mileage ratings. I was averaging 14.1 mpg in city and highway driving. A larger fuel tank this year, 36 gallons, can extend range to about 680 miles.

When it absolutely positively has to haul more than 15,000 pounds, the Denali HD diesel is a draft-horse juggernaut that seems unstoppable.