2015 Yukon Denali Gains Eight Gears, Improved Highway Fuel Economy

Most customers for the GM Yukon and Yukon XL prefer the Denali edition which now comes in a 6.2-liter V-8 version with direct access fuel injection and a much higher compression ratio. This enables the Yukon to generate 420 horsepower with 460 lb. feet of torque. The Denali’s powerful V-8 engine cuts more than a second and a half from vehicles XL's 0 to 60 time, reducing it to a whopping 5.6 seconds. The vehicle's towing capacity is still a robust 7900 to almost 8300 pounds. Not only will this version have more power to haul stuff it offers more room. The upgraded Denali editions come with 20.4 inches stem to stern, with 26.4 cubic feet of roomy cargo space. The adult third row passengers will also enjoy almost 10 additional inches of legroom.

A driver's first impression will be that the low speed drivability has improved in comparison to the old outgoing six-speed versions. While under light throttle, the gear shifts click off in a rapid fire succession, calculated to occur somewhere between 2000 to 2500 rpm. A more efficient but harder application on the accelerator can elevate the shift points to almost 3500 rpm. This is while the drive and the gear shift movements remain smooth, precise, and never jerky. When the driver floors the pedal and the 8 speed allows the 6.2-liter V-8 engine to spread its wings, while holding each gear to around 5750 rpm, which is just short of the calculated 6000 fuel cutoff.

The EPA states that the 6.2-liter GMC Yukon 4WD gains a significant 2/3 mpg city/highway compared to its six-speed earlier version.

GM also states that the 8 speed’s 7.0:1 spread of gear ratio is wider than its 6 speed units which allows a numerically higher and more efficient first gear ratio. The primary benefit is the providing of smoother takeoffs with less strain to the engine while carrying heavy loads or during towing. It also provides a sense of low speed easy to handle lightness and nimble agility during tight parking lot turns requiring multiple wheel turns. The 8 speed also enables the taller rear axle ratio to reduce engine rpm on the highway. When a driver steps on the throttle the action prompts an instant response, while the action of downshifting places the engine in the core of its torque curve. Based on test driver's experiences, the 8 speed automatic makes for a much more desired as well as improved companion for the robust 6.2-liter V-8.

Drivers may be familiar with GM’s 8 speed gear box in its Corvette model as being lighter, and more quick shifting as well as being more efficient than the 6-speed it replaced. However the scoop on how the 8L90 automatic’s gear shifting hardware was prepared for the 2015 Yukon Denali truck duty reveals that the main power flow as well as the gear architecture remains identical. However a single clutch disc design was added and a special torque converter was tuned specifically for application to the Denali truck with some truck specific gear related internal parts.

Trucks such as the Denali once needed their own bell housing for the mount for the unit to the engine, then a different type of case extension to accommodate the variables between the rear and four wheel drive versions. GM points out that the eight (8) speed in the Denali truck models is about the same weight and size as the 6L80 6 speed automatic it is designed to replace. This is a result of the truck specific bellhousing.

Though current 2015 model-year production started with a six-speed, the eight speed 8L90 automatic transmission is ready to be the new standard on GMC Yukon Denali models which are equipped with the 6.2-liter V-8.

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