The introduction of the 550-hp GL63 AMG last summer sparked a debate in our business about whether this vehicle is proof that AMG has lost its mind. We say no, no, 550 times no. Remember that AMG’s first race car was an S-class nicknamed the Red Sow. The firm is first and foremost a powerhouse: It transforms Mercedes vehicles into stealth sleds bristling with improper levels of horsepower.

To make this comparatively demure GL into an AMG, Mercedes drops in its talented twin-turbocharged 5.5-liter V-8, upgrades the transmission and all-wheel-drive system, and fits a sportier adjustable suspension. The AMG gets larger front brakes tucked inside its 21-inch wheels as well as a couple of cosmetic flourishes such as new front and rear fascias and fender flares. Sport seats fitted up front mean that, if you were so inclined, you could call this a “chairs and flares” package. We wouldn’t.

In daily use, the experience of the GL63 is much like that of the regular GL, only more urgent. Under light load, a reassuring rumble reminds occupants that the GL63 has 550 horsepower, which is 20 more than a Porsche 911 Turbo S and probably not something you want to mention to the other parents in your car-pool group. Under full throttle, a 4.8-second 0-to-60 time reminds you that the GL63 weighs 5812 pounds. Most vehicles with that much stonk weigh less. AMG’s tuning of the seven-speed automatic gives the 63 a flatulent bucksnort on upshifts, and the slowness of the rev-matched downshifts imbues them with a sort of purposeful menace.

To the two steering and suspension settings available in lesser GLs—comfort and sport—the AMG adds a third: sport plus. The range of adjustability doesn’t feel like it’s greatly expanded here compared with the non-AMG GLs, though. The widest is in the steering. It’s too light in comfort, a disconcerting feeling in something this large, heavy, and fast. We spent most of our time in sport plus, as it de-spooks the steering by turning up the resistance. The ride difference is minimal. In any mode, body control is quite good, and with its active anti-roll bars—optional on non-AMG GLs, standard here—the 63 corners laughably flatly for something so massive, up to a respectable limit of 0.84 g. And the larger brakes stop the nearly three-ton truck from 70 mph in just 162 feet, which would have tied for first in our most recent sports-sedan roundup.

Two questions keep gnawing at us. First, who needs this kind of vehicle? Not many *people. Mercedes says that just 2 percent of GL buyers will opt for the GL63. As for the second question, it has nothing to do with whether AMG should be hot-rodding SUVs. Of course it should. The SUV is the luxury sedan of the modern day. No, our second question is this: Does 13 mpg qualify as retro?

VEHICLE TYPE: front-engine, 4-wheel-drive, 7-passenger, 5-door wagon
PRICE AS TESTED (est): $130,000
BASE PRICE (est): $120,000
ENGINE TYPE: twin-turbocharged and intercooled DOHC 32-valve V-8, aluminum block and heads, direct fuel injection
Displacement: 333 cu in, 5461 cc
Power: 550 hp @ 5750 rpm
Torque: 560 lb-ft @ 2000 rpm
TRANSMISSION: 7-speed automatic with manual shifting mode
DIMENSIONS:
Wheelbase: 121.1 in
Length: 202.6 in
Width: 84.3 in Height: 72.8 in
Curb weight: 5812 lb
C/D TEST RESULTS:
Zero to 60 mph: 4.8 sec
Zero to 100 mph: 11.2 sec
Zero to 150 mph: 30.1 sec
Rolling Start, 5–60 MPH: 5.5 sec
Standing ¼-mile: 13.2 sec @ 109 mph
Top speed (governor limited): 156 mph
Braking, 70–0 mph: 162 ft
Roadholding, 300-ft-dia skidpad*: 0.84 g
*Stability-control-inhibited.

PROJECTED FUEL ECONOMY (C/D EST)
EPA city/highway: 12/16 mpg
C/D observed: 13 mpg