The biggest problem with the ML 500's handling might be the inconvenience of the heavy steering. At slower speeds the steering effort is very high, making it hard to steer in crowded parking lots. You might even find yourself turning wider than you intended to, because you didn't muscle it enough. It's possible to beat the power steering pump by turning the wheel real fast at low speeds, especially under braking.

With its V8 engine, the ML500 accelerates from 0 to 60 in 7.7 seconds. This puts it among the quickest SUVs on the market, as well as one of the thirstiest, at just 14/17 mpg in the EPA's city/highway cycle.

The flexibility of the 5.0-liter engine is impressive, with its broad torque range and whomping 325 pounds-feet. It works beautifully with the sophisticated five-speed automatic transmission. Floor the accelerator at any speed, and in a heartbeat the transmission downshifts and this 2.25-ton luxury truck gains speed, making quick, stress-free work of passing tractor trailers on two-lane roads. The transmission downshifts so smoothly all you feel is a surge of power, as if a turbocharger were kicking in.

Even better, there's the joy of Touch Shift, which allows manual shifting by nudging the lever to the left or right, with the gear displayed on the instrument panel. The transmission learns the driver's style in the Auto mode, though if you jump on it then back off to, say, make a lane change, it will downshift then hold it in the lower gear longer than you want.

The anti-lock brakes, with massive discs, ventilated in front, are impressive, and the pedal feel is as solid as the rest of the truck. The ML500 slows quicker than almost any other SUV made.

The M-Class lacks a hand brake or locking differential, two pieces of hardware that experienced off-road drivers sometimes rely on. But with 8.7 inches of ground clearance, the M-Class is capable of traversing terrain that few SUV buyers are likely to challenge. A switch on the dash triggers low range for the full-time four-wheel-drive, allowing the vehicle to creep up and down seriously steep inclines. Meanwhile, the electronic power distribution delivers grip in mud, snow, or uneven ground. The electronics apply the brakes on wheels that are slipping, and then send most of the power to those that are gripping. The M-Class can creep forward even if only one wheel has a bit of traction. Unlike a Land Rover, however, the Mercedes traction-control system can leave the M-Class sidelined when the grip goes away completely.

The ML500 performs so well, and its ride and handling are so solid, that only the wealthiest, hard-core, high-performance buyers will feel a need for the image-heavy ML55 AMG. It can accelerate from a standstill to 60 mph in 6.4 seconds. That's quick, but that will cost you another 21 grand. The engine is poked out to 5.5 liters, yielding 342 horsepower and a humongous 376 pounds-feet of torque. We drove an ML55, pushing it harder, because it will be driven very aggressively by its buyers. We found that the most fun you can have with it is holding it in second gear and charging hard through twisty sections, listening to the rise and fall of the engine's deep Benz growl. The ML55 has a 25-gallon tank, by the way. It needs it.

Suspension and shock absorber changes make the ML55 ride lower than the ML500, which helps the center of gravity. Super-wide 285/50R18 Dunlop tires provide awesome grip. But the ML 55 is still a truck, not originally intended to do the things it's modified to do. The car builders at AMG are brilliant, but they're not miracle workers. Making a tall box like the M-Class feel like much more than a modified tall box may be beyond mechanical expectations. Still, the suspension changes keep it from leaning, which is good, except now there's not much warning that you're cornering too fast, except from your own brain. Which might not always be enough.