General Motors announced that certain 2015 Chevrolet and GMC SUVs and pickups will dump their six-speed automatic transmissions in favor of new eight-speed automatic transmissions. The 2015 Chevrolet Silverado, 2015 GMC Sierra, and 2015 GMC Yukon Denali/Yukon XL Denali will all add the new transmission when production of 2015 models begins later this year. Previously, the automaker announced that the 2015 Chevrolet Corvette would also start using an eight-speed automatic instead of the six-speed unit.
Versions of the 2015 Chevrolet Silverado, 2015 GMC Sierra, and 2015 GMC Yukon Denali/Yukon XL Denali equipped with GM’s 420-hp 6.2-liter EcoTec3 V-8 engine will benefit from the new 8L90 eight-speed. According to GM, the change will allow a lower rear axle ratio that will lessen engine rpm at highway speeds, while a numerically higher first-gear ratio should improve acceleration and towing performance.
Although it adds two speeds, the new transmission is almost the same size and weight compared to the outgoing transmission. In the 2015 Chevrolet Corvette, the 8L90 transmission is eight pounds lighter than the old six-speed, in part due to aluminum and magnesium components in the housing.
A spokesman from Cadillac also confirmed to Automobile that the 2015 Cadillac Escalade will receive the same treatment in the not-so-distant future, ditching its six-speed for the 8L90 eight-speed automatic transmission.
What this means for EPA-rated fuel economy is still uncertain, but GM promises to reveal more details as the vehicles approach production in the fourth quarter of this year. Currently with the 6.2-liter V-8 and six-speed automatic transmission, the 2014 Chevrolet Silverado and 2014 GMC Sierra are rated for 15/17/21 mpg (city/highway/combined) with rear-wheel drive, while the 2014 GMC Yukon XL and 2014 Cadillac Escalade get 14/16/18 mpg with rear-wheel drive. It's likely all those figures will improve slightly thanks to the addition of the new automatic transmission.