Truck people talk frames and parts because they're the foundation.   On the Sierra HD the foundation includes things like forged steel upper and cast iron lower front suspension arms like pieces used on older Land Rovers and the Mercedes Gelaendewagens rather than the aluminum and stamped steel of lightweight pickups.   Everything was upgraded for 2011, right down to the bolts that hold the wheels on.  

Adding bigger parts is easy.   What makes the GMC HD noteworthy is that the increase in capability comes with no significant sacrifice in ride quality, cab comfort, handling or control.   GMC claims diesel highway fuel economy is up 11 percent, quoting range on the 36-gallon fuel tank that suggests about 18.5 mpg; but honestly the only time you should be highway cruising in an empty HD is after you've delivered the cargo or trailer somewhere.   No mention of city mileage, probably because the truck is 300-400 pounds heavier than its predecessor.   We observed 10 mpg in the largest HD diesel pulling a four-ton trailer.  

That gasoline engine is the purchase-cost choice and best used when routine heavy towing or high mileage aren't on the agenda.   Opting for the $100 higher-numerical 4.10:1 axle ratio is worth every penny and raises the tow rating considerably.   We saw a bit more than 12 mpg on a highway leg in an unloaded 2500-series gas engine.  

All other buyers should strongly consider the diesel with twice the torque output and notably better mileage and work ratings.   It is quieter but the last GM HD was already relatively quiet, and like Ford but unlike Ram, it uses DEF for the emissions system.   This is filled underhood and may need to be done only at service intervals but is available at fuel depots and parts stores if you drive hard.   Running out will not stop the truck, but if you ignore warning messages it eventually will not restart.  

Pickups of yore tended to buck like broncos on uneven surfaces like turnpike expansion joints, with the bed trying to bounce one direction and the cab the other.   Often a function of wheelbase, this can't be completely eliminated in a long vehicle like a Sierra HD, but it does an admirable job of mitigating the motion.   Longer cabs get special body mounts to aid in that regard, though we found the regular cab gave a good accounting of itself; with the diesel's 700-mile-empty claimed range, it's entirely possible a base manual seat would wear you out before any ride issues did.  

There's heft to the feel of a Sierra, from the way it takes big bumps to the steering and throttle inputs but this should not be construed as effort on the driver's part.   Its handling characteristics are benign and amount to basic plowing if you push too hard.   All-terrain tires give better grip on dirt roads, at the expense of steering precision and noise on tarmac.   Optional 20-inch wheels look good but we'll stick to standard 17s and 18s for numerous reasons, including ride and replacement cost.  

Like all big 2WD pickups the Sierra uses all-vented disc brakes with ABS, and independent front suspension.   Of the full-size pickups, only the GM heavy-duty pickups use the same design on 4WD models as on 2WD versions.   This means the 4WD HD models from GM have a lower nose and more responsive steering than their Ram and Super Duty counterparts.   Again, like any big pickup, the tail is prone to kick over impacts with an empty bed; the Sierra is similar to others although it may feel it has more kick because the front is softer.   Apart from turning circle and size, it takes no more effort to drive this than to drive any other GMC.  

The optional integrated trailer brake controller will apply your trailer brakes smoother than any aftermarket controller and works in concert with the Sierra's braking system.  

The diesel engine has an exhaust brake function in the turbocharger, and the Allison transmission uses grade control logic to help maintain chosen speeds, even using cruise control on up- and down-grades.  

The 2.5-inch receiver hitch allows conventional trailer ratings up to 17,000 pounds, and the maximum for fifth-wheels is almost 22,000 pounds, both segment leading.   The strongest Sierra HD will haul more than 29,000 pounds gross combined: the truck, fuel, passengers, cargo, and loaded trailer.   That means, and this applies to all domestic pickups, that a Sierra rated for a trailer of 21,000 pounds and a load of 5,800 pounds can't do both simultaneously.