The GL class came to be in 2007 in the form of the GL450, and was based on the decades-old squared-off G-class SUV. The GL has most of the off-road capabilities of the military-style G-wagon, plus third-row seating, more creature comforts, and 500 more pounds of towing capability. The GL class has grown from one model to three, including an ultra-luxury edition and a low-emissions diesel. The big news for 2009 is the turbocharged GL320 BlueTEC 3-liter V6 diesel engine. It puts out 210 hp and 398 lb-ft of torque, and is still capable of 17 mpg city and 23 mpg highway. The BlueTEC achieves 50-state emissions certification by cleaning the diesel emissions at the rear of the car using a combination of particulate filters and a urea additive Mercedes calls "AdBlue." The GL450 (starting at $59,200) has a 4.6L V8 mounted longitudinally, with 335 hp and 339 lb-ft of torque. The GL550 (starting at $81,300) has a 5.5L V8 with 382 hp and 391 lb-ft of torque. All three models have a 7-speed automatic transmission, full-time 4-wheel drive, electronic brake assist, adaptive variable suspension, stability control, traction control, tire pressure monitoring and automatic load leveling. Many of the features that are standard on the GL550 are options on the two other variants, such as leather seats, auto-dimming rearview mirror, navigation system and electronic parking aid. All GLs have airbags all around, the Pre-Safe system, keyless entry, alarm system and vehicle theft tracking. The GL320 and GL450 have an 8-speaker CD/MP3 stereo, birdseye maple trim, and halogen headlights. The GL550 upgrades these to standard harmon/kardon 11-speaker CD/MP3 stereo with Sirius satellite radio, burl walnut trim and adaptive bi-xenon lights. Only the GL320 and GL450 have packaged options available. The Heating Package, for example, adds heated rear seats and steering wheel -- both of which are standard on the GL550. The Premium packages for the GL320 and GL450 add options such as bi-xenon headlights, a backup camera and 3-zone climate control. There's also a GL Appearance package to add a little extra exterior style to these two models. A rear-seat DVD entertainment system is an option for all three GLs. The options list for the GL550 is pretty short, as it already comes standard with all of the options available for the GL320 and GL450. Active ventilated front seats are available as is birch trim instead of walnut, and premium Nappa leather upholstery. Mercedes upgraded last year's CDI diesel engine to the GL320 BlueTEC V6 diesel, which scrubs the emissions as well as delivering better fuel economy. All three GL versions get Mercedes' Pre-Safe system, which anticipates collisions and takes steps to protect the passenger. Full-size, 7-passenger luxury SUV; new BlueTEC diesel engine for better mileage and 50-state emissions compliance; bigger on the inside than it seems from the outside The GL series comes in three trim levels: the GL320 with the BlueTEC V6 diesel engine; the GL450 with a 4.6L V8; and the GL550 with a 5.5L V8 with appearance touches such as 21" AMG alloy wheels and a huge Mercedes medallion on the grille. Each model has 4-wheel drive, a 7,500-lb towing capacity, a 7-speed transmission, and the Pre-Safe system.