The GMC Sierra 2500 HD is solidifying its reputation as a tough as nails truck with a new 6.6-liter Duramax V-8 turbo diesel engine that produces a whopping 765 lb.-ft. of torque at 1,600 rpm.

Also, a new Denali line is offered for the first time this year on a GMC heavy-duty truck.

The new diesel engine is more powerful than its predecessor, delivering 397 horsepower, compared to the 365 horses from the 2010 model. It also produces 63 percent lower emissions than the 2010.

The 2500 HD also has an incredible range of up to 680 miles on a single tank of fuel, saving busy drivers time. Of course when you do stop, it’ll take a while to put the 36 gallons of diesel in the tank. The EPA does not supply mileage estimates on large trucks, but we managed 17.1 miles per gallon in combined driving during our week with the test Sierra. GMC says the diesel engine is approved to run on B20 biodiesel, and that it gets 11 percent better fuel economy than last year’s version.

The new Duramax 6.6-liter also has a “smart” exhaust brake feature that enables controlled vehicle slow-down on downhill grades without activating the brakes. GMC says the new engine is quieter, and it is. But it’s not like some of the incredibly quiet diesel engines in cars. This is a big honkin’ truck with a big honkin’ engine.

The Denali version provides a luxurious cabin with lots of comfort features like heated and cooled leather seats, dual-zone air, power everything, Bose premium sound on XM Satellite Radio, adjustable pedals and a leather-wrapped heated steering wheel. But make no mistake, this is still a workhorse truck.

At 78-inches tall, the truck is as tall as Kobe Bryant, and taller than John Wayne. At 240 inches of overall length, the 2500 fits parking spaces better when it is backed in.

And when it comes to work, the GMC delivers. The Denali 2500 HD with 4WD can tow up to 21,700 lbs. when properly equipped (conventional towing is 17,000 lbs.), and has a payload capacity of 4,192 lbs., according to GMC.

The new Denali line is distinguished by the iconic 4-bar chrome grille with round air inlets and the big GMC logo. It also sports body colored bumpers, chrome door handles chrome accents and 18-inch polished forged aluminum wheels. Our test truck had the optional 20-inchers, which really add to the truck’s profile. The truck is offered in black, stealth gray and white.

The new Denali HDs are crew cabs available only in the 2500 series (Ø-ton) in 2WD or 4WD, or the 3500 series (1-ton) 2WD or 4WD. The standard engine is the 6.0-liter Vortec gas V-8.

Along with the upscale cabin, the truck has all the current consumer connectivity, including available mo-bile WiFi, USB ports, Bluetooth, OnStar and navigation.

The ride in the Denali 2500 is stiff thanks to the fully-boxed frames with increased cross sections. Bending and beaming stiffness is increased by 92 percent, according to GMC.

Not rated for safety by the government, the Sierra Denali 2500 4WD is equipped with Stabilitrak, four-wheel anti-lock disc brakes, airbags with available side curtains, trailer sway control and hill start assist.

With about $14-grand in options, including the $7,195 Duramax turbo diesel and the $1,200 Allison 6-speed automatic transmission, the bottom line on the upscale Sierra Denali 2500 4WD crew cab was $61,774, including $995 in destination charges. But this, folks, is a big tough truck with a luxurious Denali package inside.