The 2015 Mercedes-Benz GL-Class is offered in four different models: the GL350 BlueTec, the GL450, the GL550 and the GL63 AMG. Engines are the key difference between the four: GL350 BlueTec models come with a 3.0L turbo-diesel V6 engine that makes 240 horsepower and 455 pound-feet of torque, while GL450 models include a new 3.0 turbocharged gasoline V6 making 362 hp and 369 lb-ft. GL550 models include a 4.6L V8 rated at 429 hp and 516 lb-ft, while the GL63 AMG gets a 5.5L bi-turbo V8 making 550 hp. The BlueTec diesel engine is one of the stars of the lineup, as it manages more low-rpm torque -- what matters for towing and full loads -- than the GL450 V6. Yet with EPA fuel economy ratings of 19 mpg city and 26 highway, this 7-passenger SUV is just as efficient as some much smaller crossovers. It's also 50-state certified, thanks to a system that injects a urea solution Mercedes-Benz calls "AdBlue" into the exhaust flow. The new V6 delivers the same power as the 4.6L V8 it replaces while also improving fuel economy. And the big V8 is smooth and high revving, with a thick piston-crown design to handle the extra power. In addition, both the V6 and V8 gasoline engines now feature stop-start technology to aid overall economy. Throughout the lineup, the GL-Class has a 7-speed automatic transmission that teams with 4MATIC 4-wheel drive and has been optimized for better mileage and durability plus responsiveness and refinement. In each case, it makes the most of engine power for passing or strong acceleration, yet it's smooth and unobtrusive during relaxed driving. The GL-Class is Mercedes-Benz's own alternative to the truck-like G-Class and it therefore offers a more car-like driving and ownership experience. The front seats in the GL-Class can be equipped with heating, ventilation and multi-contour functions that not only massage you but give you added support in corners. The GL-Class has second-row seats that are adult-sized and have a power-operated access feature to make it easier to reach the third row, which is split 50/50 and can be flipped forward -- as can the second row. A height-adjustable AIRMATIC suspension system is included in all GL models, and it helps soak up road shocks while keeping the body level. Electromechanical rack-and-pinion steering with speed-dependent power assist brings a confident feel both at high speeds and trail speeds. Meanwhile, the GL-Class retains its truck-caliber abilities, with excellent towing capability as well as off-road chops--when you check the right option boxes. With the On & Offroad Package, the GL-Class gets additional underfloor paneling, a dual-range transmission, and underrun protection for the engine, as well as a version of the AIRMATIC suspension that allows more ground clearance -- up to 12 inches, with a water-fording depth of 23.6 inches. The latest version of Mercedes-Benz' COMAND screen-based interface is part of the instrument panel of every new GL-Class. COMAND manages entertainment and includes HD Radio, Bluetooth hands-free calling and Bluetooth audio streaming, while an iPod interface, satellite radio and enhanced voice control are available. A hard-drive navigation system is optional and it can incorporate real-time Sirius traffic information and Zagat restaurant ratings. A rear-seat entertainment system is also optional and includes two 8-inch screens plus wireless headphones and a DVD player, while the top entertainment possibility is a Harman/Kardon Logic7 surround-sound system with 830 watts and 14 speakers. The GL-Class is also loaded with active-safety features. Attention Assist looks for signs that the driver may be drowsy, while Collision Prevention Assist warns the driver of a possible collision and primes the brakes. Active Parking Assist is also available and helps automatically steer the vehicle into a spot while the driver controls acceleration and braking. Other optional active-safety features include Active Lane Keeping Assist, an Active Curve System and a 360-degree Surround View camera system. A Panorama Roof is also available. Many of these options are grouped in packages and two Premium Packages add hard-drive navigation, memory front seats, interior ambient lighting, illuminated door sills and audio upgrades. Three-zone climate control, heated rear seats, a heated steering wheel and stylish real woodgrain trims are also on the options list.