Buick and GMC posted sales gains in December, while Chevrolet was flat and Cadillac continued its desperate struggles as nearly every model in the luxury brand’s stable was down dramatically relative to December 2016.

As a whole, General Motors sold 308,248 vehicles in the U.S. in December, a 0.4% dip from December 2016 based on the daily sales rate. There were 27 sales days in December 2016 and 26 last month. For the year, GM notched 3,000,147 U.S. deliveries, a 1.4% decline from 2016, according to WardsAuto data.

Cadillac deliveries last month plunged 25.9% compared with like-2016 based on DSR, and the year-end tally was off 8.0% to 156,440 vehicles.

The only silver lining for Cadillac was growth for the XT5 5-passenger CUV, which went on sale in spring 2016. In 2017, its first full year on the market, the XT5 notched 68,312 deliveries, up from 39,485 the prior year. Far and away, the XT5 was Cadillac’s top seller, accounting for 44% of its 2017 sales. For the month, however, XT5 sales were down 3.8% daily from December 2016.

Cadillac’s other gainer for 2017, its first full year in the market, was the CT6 flagship sedan, which first arrived in showrooms in spring 2016 and was up 15.0% to 10,542 units last year. Throughout 2017, the CT6 was badly outsold by the Mercedes S-Class, BMW 7-Series and Tesla Model S.

Buick deliveries were up 8.7% in December based on DSR to 22,285 units on the strength of the Enclave 3-row CUV (+45.5% to 5,326 from like-2016) and smaller Envision, which is assembled in China and arrived in 2016. Last year, its first full year in the U.S. market, the Envision recorded 41,040 deliveries. However, Buick’s full-year total was down 4.5% to 219,231 units from 2016.

Like the rest of the industry, Buick is riding the wave of crossover popularity. Together, the Enclave, Envision and compact Encore CUV made up 81% of Buick’s 2017 sales, compared with about two-thirds in 2016.

Buick redesigned the LaCrosse sedan last year (winner of a 2017 Wards 10 Best Interiors trophy last spring), and its 2017 tally in a market lukewarm to conventional sedans was a mere 20,161 units, down 26.9%.

The all-new ’18 Regal also is arriving now in showrooms with three body styles: Sportback 5-door, GS sedan and TourX estate car. With the previous-generation Regal ramping down, 2017 deliveries for the sedan were off 41.7% to 11,559 units.

GMC, well positioned with premium trucks and utility vehicles at the height of their popularity, grew its December sales 5.0% on the strength of the fullsize Yukon (+41.2% from like-2016 to 8,531 units) and Yukon XL SUVs (+13.9% to 6,421) based on DSR.

Also up in December was GMC’s best seller, the Sierra fullsize pickup (+17.9% to 26,436 units) based on DSR. But for all of 2017, Sierra sales were down 1.7% to 217,943 from prior-year.

GMC’s year-end tally was up 2.6% to 560,687 vehicles on the strength of the redesigned 3-row Acadia CUV, which was up 25.8% to 111,276 units in 2017, its first full year. The Savana van also improved in 2017 to 29,679 units, a 44.0% gain.

Chevrolet sold 206,513 vehicles in December based on DSR, up 0.8%. For the year, the bowtie brand was down 1.5% to 2,063,789 units.

Bright spots for Chevy included the new Equinox midsize CUV, which posted a 25.2% gain over December 2016 based on DSR, as well as a 19.9% improvement for full-year 2017, to 290,458 units. The brand’s best-selling Silverado fullsize pickup was up 29.5% in December (Silverado’s best month ever), while the full-year growth was a modest 1.9% to 585,864 trucks.

The redesigned Chevy Traverse also did well, with daily sales in December rising 23.2%. For all of 2017, Traverse deliveries were up 5.8% to 123,506 CUVs.

Volume for the all-electric Bolt EV also picked up dramatically in December to 3,227 units, for a full-year tally of 23,297. GM says December was Bolt’s best sales month since launching earlier in the year.

Overall, Chevrolet says its average transaction price for the month was the best ever at more than $34,000. Since the end of 2014, the brand says its retail share has grown from 10.2%, according to Polk registration data, to an estimated 11.2%.

Across all brands, GM says its average transaction prices (which are net of incentive spending estimates) were more than $35,400 for the year and surpassed $38,000 in December. Both are records, and above the industry average of $31,600 for the calendar year, the automaker says.

GM says it exceeded its target in reducing year-end inventories to 63 days’ supply. Inventories were 752,554 units, down 90,000 from a year ago.

Mustafa Mohatarem, GM’s chief economist, forecasts 2018 total vehicle sales (including medium and heavy trucks) to exceed 17million units for the fourth year in a row. Light-vehicle sales are forecast to be in the high 16 million-unit range.

“In 2017, we had solid GDP growth and good news on employment, wages and consumer sentiment, which helped deliver very strong retail sales for the auto industry,” he says. “This year, many consumers will see their take-home pay rise because of tax reform. That will keep the broad economy growing, and help keep sales at very healthy levels even as the Fed increases interest rates.”

On a retail basis, 78% of GM sales are now trucks and crossovers, compared with an industry average of 65%, the automaker says.

tmurphy@wardsauto.com