Getting into the 4WD 3500HD (dualie) diesel, it was instantly clear that the Denali's interior is not nearly as brash as in the King Ranch. The truck's interior is tasteful and attractive, but if you want the large badges and unique leather hue of the King Ranch, you might find this too understated. Seats are comfortable during long drives, and all the controls were easy to reach while driving. The cabin was roomy, and for those familiar with GM's basic layout of truck interiors, there are no real surprises here.

What was a surprise was how fast the truck felt. We used it to tow 12,000 pounds up a 16-percent grade, where even semi-casual drag races against competitive trucks showed that the Denali pulled away. The Sierra HD had no trouble putting the power to the wheels. Even with 765 pound-feet of torque, there was no wheelslip, which was not always the case with other trucks in this competitive set.

Power came effortlessly, and with a trailer in tow, it still felt like a performance truck. Later that day Motor Trend/Truck Trend technical director Frank Markus put the truck through our battery of performance tests and confirmed our seat-of-the-pants theory: This truck doesn't just feel fast -- it is fast. It reached 60 mph in just 7.7 seconds and went through the quarter mile in 16 seconds flat at 85.5 mph. It weighs 8100 pounds, and its 0-to-60-mph time is comparable with those of a Dodge Challenger (V-6-powered), Mazda3, or Acura TSX. And the last time we checked, none of those cars could tow 21,100 pounds. Braking from 60 mph took 143 feet.

After a full day of driving -- from early in the day until long after midnight, on two-lane country roads and highways, in rain that fell in sheets and bright sunshine -- the Sierra Denali HD impressed us. The truck is much more refined now, with a quieter cabin than ever before, and the ride is smooth and comfortable. This is a truck you could drive all day, all week, with a heavy load in back, and you'd ride in comfort, with total confidence. Oh, and the fuel economy, which we recorded as a combination of driving while towing and with the truck unloaded, was 13.6 mpg.