2015 GMC Yukon XL SLT

The 2015 GMC Yukon XL SLT was unveiled Thursday in Los Angeles along with other models. (General Motors / September 12, 2013)

In a pair of news conferences on either side of the country Thursday, General Motors pulled the covers off the latest generation of its very large -- and very profitable -- lineup of full-size SUVs.

In New York, GM’s everyman brand Chevrolet debuted the all-new 2015 Tahoe and Suburban. Simultaneously in Los Angeles, the more upmarket GMC label had the 2015 Yukon, Yukon XL, and Yukon Denali on display. 

GM promised greater efficiency, safety and refinement for the entire lineup when it goes on sale in the first quarter of 2014. This, in an effort to maintain GM’s stranglehold on the segment. 

PHOTOS: GM's 2015 full-size SUVs announced

"This is an important and profitable segment and we have set the bar high to ensure we provide our customers with great quality and performance they expect and deserve,” said Dan Ammann, GM’s vice president and chief financial officer. 

Through August of this year, the previous generation of GM’s giants have accounted for 74% of all full-size SUV sales in the U.S., the automaker said. About 125,000 units have been sold. These high volumes have meant big profits for the automaker, which ranked as the world’s largest in 2012.  

The 2015 models will all share a platform and base powertrains, though the larger Chevrolet Suburban and Yukon XL models have a wheelbase that’s 14 inches longer than the Tahoe and Yukon. 

All models grow two inches longer for 2015, dividends that second-row passengers will notice in two additional inches of legroom, GM said. Both the second and third row of seats will now fold flat.

Base engines remain a 5.3-liter V-8, though significant improvements have been made to increase both power and efficiency. Horsepower rises to 355 from 320, while torque jumps to 383 pound-feet from 335 pound-feet. 

This engine now includes fuel-saving features like cylinder deactivation and direct-injection. EPA figures haven’t been released yet, but GM said it expected a bump in highway fuel economy over the previous generation.  

The higher-end Yukon Denali will come with a 6.2-liter V-8 that makes 420 horsepower and 460 pound-feet of torque. It will probably share this engine with the next generation Cadillac Escalade that will debut in the coming weeks. 

All the GM SUVs announced Thursday will come with a six-speed automatic transmission.

The vehicles’ exteriors have also undergone a thorough massaging. Each features a more squared-off profile. Larger, bolder grilles up front are flanked by more expressive headlights that wrap around the side or top of the quarter panels. 

This softer look up front allows for greater aerodynamics and efficiency on the highway, GM said. An aluminum hood and rear liftgate help reduce weight.

Pricing details were not announced. The vehicles will be built in the automaker’s Arlington, Texas, assembly plant, GM said. 

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