General Motors has added an eight-speed automatic transmission to its 2015 GMC Yukon Denali and Yukon XL Denali models that improves fuel economy from the six-speed offered with the 2014 models.

The large SUVs will improve their EPA-rated fuel economy by about 15 percent, when the new 8L90 transmission is paired with the 6.2-liter EcoTec V-8 carried over from the 2014 model year. GM also offers a 5.3-liter V-8. Fuel economy improvement will vary slightly with the rear-wheel and four-wheel drive models.

The rear-wheel 2015 Yukon Denali achieves an EPA-rated 22 mpg highway, 15 mpg city, and 17 mpg combined. The four-wheel model achieves 21 mpg highway, 15 mpg city, and 17 mpg combined.

The four-wheel 2014 Yukon Denali achieved an EPA-rated 18 mpg highway, 13 mpg city, and 15 mpg combined, while the rear-wheel model achieved 18 mpg highway, 14 mpg city and 16 mpg combined.

The new 8L90 transmission provides a wider gearing spread that allows for the use of a 3.23:1 rear axle ratio, which reduces engine speeds and fuel consumption especially during highway cruising.

Tow ratings are unaffected by the move. The Yukon Denali can haul 8,400 pounds, while the Yukon XL Denali can tow 8,100 pounds.

GM has set retail pricing on the models at $64,965 for the Yukon Denali and $67,665 for the Yukon XL Denali. The vehicles have arrived at dealerships.

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2015 Chevrolet Tahoe and GMC Yukon Denali