The GLS, a full-size SUV, is back unchanged and just as versatile and luxurious as ever for 2018. The GLS 450 4MATIC (362-horsepower, twin-turbo V6) and GLS 550 4MATIC (449-horsepower, twin-turbo 4.7L V8) are both equipped with a nine-speed automatic gearbox. The AMG GLS 63 4MATIC (hand-built 577-horsepower, twin-turbo 5.5L V8) remains top dog with its impressive torque transmitted to all four wheels by a seven-speed gearbox.