People walk by a Ford Escape SUV displayed during the media day for the Shanghai auto show in Shanghai, China, April 16, 2019.

DETROIT – U.S. auto sales during the third quarter for the Big Three Detroit manufacturers were mixed with General Motors pulling ahead of the pack. A falloff in demand for Ford's popular pickups drove a decline in its overall sales.

GM's U.S. sales rose 6.3% in the third quarter over the same period last year while Ford Motor's sank by 4.9% and Fiat Chrysler's were flat, according to data release Wednesday by the three automakers.

Shares of all three were all trading in the red Wednesday afternoon amid a broader market downturn. The Institute for Supply Management released a weak manufacturing report Tuesday that showed a possible economic slowdown attributed to the escalating trade war.

Shares of GM, which is in the middle of a union strike, tumbled by about 4% Wednesday afternoon. Ford and Fiat Chrysler were both down by about 3%.

Cox Automotive reports U.S. auto sales were estimated to be down 11.7% in September, dragging industry sales down 1.4% through the first nine months of the year.

Pickups dominated Wednesday's car data. GM's redesigned Chevrolet Silverado and GMC Sierra pickups saw double-digit sales increases that helped offset a 38% declines in car sales. The company's overall truck sales, which include SUVs and vans, rose 8.8% during the quarter. Sales of crossovers also increased 28.3% for the quarter, largely thanks to the introduction of new models.

Ford, meanwhile, saw sales of its highly-profitable F-Series pickup line tumble 6% in the quarter, dragging the truck's sales during the first nine months of the year down 2.4% as the company competes against newer models from GM and Fiat Chrysler.