If the new Ford F-Series Super Duty is the immovable object, then the new GMC Sierra HD and Chevrolet Silverado HD are the irresistible forces.

With both vehicles all-new for '11, these behemoths are bound to clash like gladiators as they arrive in the market at roughly the same time.

During a recent GM test drive in Cumberland, MD, following an extended turn in the Ford Super Duty, we're predicting one ferocious battle, as the trucks are evenly matched in most regards.

The wild card is Chrysler Group LLC, which launched an all-new heavy-duty Ram last year, with towing capabilities that come up shy of the Ford and GM offerings.

Both the Silverado and more upscale Sierra are work trucks, plain and simple. Need a commuter vehicle? Look elsewhere. The intended purpose is hauling and pulling things. Big things.

While GM trucks come available with a 6.0L Vortec gas V-8 making 360 hp and 380 lb.-ft. (515 Nm) of torque, it's the 6.6L Duramax diesel that inspires awe. The oil burner boasts 397 hp and a devastating 765 lb.-ft. (1,037 Nm) of twist.

Eye-popping torque figures are common in this segment. The new Super Duty diesel launched with 735 lb.-ft. (997 Nm) earlier this year, and Ford recently announced a software tweak that boosts torque to a staggering 800 lb.-ft. (1,085 Nm).

But as much as it is a “mine-is-bigger-than-yours” contest between Ford and GM, engine output is a top purchase decision in the heavy-duty pickup market.

To demonstrate the trucks' Herculean strength, GM engineers cobbled together a series of grueling tests.

We were invited to take the wheel of a Silverado 2500 HD crew cab (in which we spent the bulk of our time) and pull a trailer weighing 9,500 lbs. (4,309 kg) and measuring nearly twice the length of the truck, itself. For context, that's the collective weight of nearly four Chevy Aveo sedans.

This test, GM says, represents how actual owners use their trucks — for pulling prized ponies or large equipment. The truck's maximum tow rating is a whopping 17,000 lbs. (7,711 kg).

From a standstill, the trailer's heft is evident, as the Silverado groans with displeasure as it builds up speed. Once at cruising velocity, however, the trailer is barely noticeable.

That is, until we encounter the serious slopes that are common in Maryland along the logging roads.

Climbing steep grades takes a little coaxing. But the descents make the hair on the nape of the neck stand up, as the full heft of the nearly 5-ton (4.5 t) trailer bears down on us.

Before we have a chance to stomp on the Silverado's enormous 14-in. (35.6-cm) brakes, the truck's new “smart” exhaust brake system kicks in.

By controlling the variable-geometry turbocharger and compression of the engine, the driver-selectable feature generates backpressure, slowing the vehicle in a steady and predictable manner without touching the brakes.

Ram offers the feature as standard equipment, and it's available also on Ford's Super Duties — a good thing because we find the technology essential while towing heavy loads. Unfortunately, it's not available in GM models equipped with the gas engine.

With the trailer disconnected, the Silverado displays surprisingly refined driving characteristics. More so than Ford's Super Duty.

The Chevy chassis is remarkably stiff, helping to improve the ride. GM says the bending stiffness of the frame has been increased 92%, and torsional stiffness is enhanced by a factor of five, compared with the outgoing model.

The Silverado HD's new chassis comprises 11 fully boxed frame assemblies to meet a broad mix of buyers, from those seeking the conventional pickup with cab and box to dually and chassis-cab customers.

The Allison 1000 6-speed transmission proves a good match for the 6.6L diesel. Shift points are imperceptible, and the transmission never seems to hunt for gears.

For '11, engineers redesigned the independent front suspension, beefing up components to a 6,000-lb. (2,721-kg) front gross axle-weight rating. That's a 25% improvement over the previous model, making all 4-wheel-drive versions capable of snow-plow duty.

In the rear, GM replaces the pickup's semi-elliptical suspension design with a new asymmetrical leaf-spring setup.

The revised suspension goes a long way in ensuring small imperfections in the road aren't transferred to the passenger compartment.

Because of their monumental output, HD pickup manufacturers are not required to estimate fuel efficiency based on Environmental Protection Agency criteria. Mileage varies, of course, depending on terrain, speed and load.

But with no trailer and little cargo, the Duramax diesel is capable of 19 mpg (12.3 L/100 km) in mostly highway driving, according to our evaluation. Not too shabby, considering a curb weight of 7,208 lbs. (3,269 kg).

Overall, the mechanicals are impressive. The same cannot be said for exterior styling.

The Ford Super Duty may be over-the-top with its gargantuan grille and dinner plate-sized Blue Oval badges, but it fits the truck's hulky proportions.

The Silverado's styling leaves us wanting. It looks too much like the light-duty truck and instead needs to set itself apart as an entirely different beast.

The interior is nicely appointed with quality materials. But Ford's interior is more eye-pleasing, and the Ram HD's even more so.

GM offers for the first time a Denali version on its heavy-duty GMC Sierra, and it's more attractive inside and out than the less-expensive Chevy.

With its distinctive 4-bar chrome grille up front and brushed-aluminum accents and soft-leather seats inside, the Denali should serve as a blueprint for the next-generation GM trucks.

Both Ford and GM heavy-duty pickups now are hitting dealers en masse. Those in the market for such a vehicle will be sorely tempted to forego brand loyalties.

Let the clash of the titans begin.