General Motors and Fiat Chrysler Automobiles reported hefty sales declines for their big trucks, a troubling sign for a lucrative segment that had been holding up well as the broader U.S. auto market shrinks.

Bloomberg News reported that deliveries of Fiat Chrysler’s Ram pickup and GM’s Chevrolet Silverado and GMC Sierra trucks each fell by at least 15% in February. While the industry-leading F-Series line bucked the trend with a small increase, Ford’s total sales still missed estimates.

Detroit’s pickups are some of the auto industry’s most profitable model lines, commanding average prices exceeding $40,000. The tepid demand for trucks — which consistently rank among the top-sellers in the U.S. market — was a major contributor to total deliveries potentially slowing down last month to the most sluggish pace since Hurricane Harvey ravaged dealerships across the Texas Gulf Coast in August.

“It’s looking like it was a challenging month,” said Jeff Schuster, senior vice president of forecasting for LMC Automotive. “It’s a continued, steady softening of the market.”

Most major carmakers fell short of expectations and posted steeper decreases than analysts were projecting. The annualized rate of sales, adjusted for seasonal trends, probably slowed to 16.9 million cars and light trucks last month, according to a Bloomberg News survey. That would be down from 17.5 million a year earlier.

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