With a massive 4.6-liter V8 that outputs 449 horsepower and 516 foot pounds of torque (335 kW, 700 Nm), the 2017 Mercedes-Benz GLS550 is a beast of a sport utility. Signature Mercedes good looks and sports car-like driving mark this SUV out from the rest.

We were consistently impressed during our week in the 2017 Mercedes-Benz GLS550, though that doesn't mean the big SUV has a perfect scorecard. Last year, this was the GL-Class sport utility, but Mercedes-Benz wanted to tie it in with the company's flagship S-Class sedan, making the GL the flagship of the carmaker's SUVs, so an S was added. The other changes for 2017 are relatively minor, with some engine tweaks for more power, a bit of exterior refinement, a newly-standard nine-speed automatic, and a better infotainment system. We were a bit underwhelmed by some of the interior materials choices, especially in plastics, with some being a touch on the unrefined side for the German luxury make, we think.

We drove the big V8-powered GLS550 model, but there is also the GLS450 with a 3.0-liter turbocharged gasoline V6 outputting 362 horses (270 kW) and 369 lb-ft (500 Nm). Both the GLS450 and GLS550 have the aforementioned nine-speed auto-trans as standard. The AMG GLS 63 not only separates its numbers from the model, but also separates itself with a huge 5.5-liter V8 that screams out 577 horsepower (430 kW) and 561 pound-feet (761 Nm) of torque through an all-wheel drive equipped seven-speed automatic transmission.

At best, the GLS-Class returns 22 mpg (10.7 l/100km) on the highway with the GLS450 and at worst, the AMG GLS 63 sucks down fuel at a 14 mpg (16.8 l/100km) on the combined cycle. We averaged barely 14 mpg combined in the GLS550 4Motion during our week of testing. Most of that was highway and freeway driving, at altitude in Wyoming and Colorado.

That said, if you're spending the price of the average house in much of rural America (about US$95,000 to $100,000) on your SUV, you probably aren't all that concerned about fuel economy. Mercedes-Benz knows this and put a large fuel tank in the GLS to compensate (26.4 gallons, 100 liters); because price at the pump may not be a factor, but how often you pump is.

Almost everything about the drive quality, road feel, and interior excellence and ambience of the GLS is excellent. A few things seem out of place or give the impression of having been last-minute add-ons in the GLS' driver's cockpit, however. The cruise control dongle, for example, is set on the left, lower side of the steering wheel's column and is difficult to see. It takes time to learn the settings (set, accelerate, resume) and it was not unusual for us to turn on the turn signal (just above it) rather than reset the cruise control while driving. Similarly, the Kommand knob for the infotainment interface is placed right about where the driver's hand wants to be when an arm is resting on the right-side armrest. That meant occasional, unintentional bumps of the infotainment interface.

On the up side, everything else about the Mercedes-Benz GLS550 is top shelf. The interior has several options, depending on packaging, with the 550 model having a 10-way power driver's seat, multi-color ambient lighting throughout, navigation with real-time traffic, Apple CarPlay, and the Park Assist package with parking sensors and parallel parking assistance. Three-zone climate, heated/ventilated front seating, and a 13-speaker Harmon Kardon sound system are standard. Massaging front seats are also standard in the GLS550, and are well worth having.

On the road, the 2017 GLS550 delivers a smooth ride and excellent all-round capability. It comes standard with adaptive suspension dampers and an air ride system. These both add comfort to smooth the ride and create stiffer lean when cornering and maneuvering – the best of both worlds when it comes to luxury sport driving.

This Mercedes drives smaller than it is, feeling more like a tall sports car than a big SUV. The satisfying growl from the big V8 when the throttle is pressed and the push back into the seats on acceleration are the reason buyers look to the sporty GLS550. We found nothing to complain about in the on-road experience with this Mercedes.

Away from the tarmac, the 2017 Mercedes-Benz GLS550 is competent and can do most general off-pavement tasks. Ours was equipped with road-going winter tires, so grip off-pavement was limited and truth be told, this is not meant to be a pure off-road machine.

Overall, the 2017 GLS550 is an erudite luxury crossover that stands alone in its segment. There are few comparisons, in fact, with most other luxury makes having gone another direction (such as the capable luxury of the Infiniti QX80), leaving the big Mercedes alone as the only performance machine in the segment.

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