Unspecified "parts issues" slowed shipments of Ford's 2017 Super Duty pickups in late summer, but Ford is ironing out these issues at its Louisville, Ky., assembly plant, according to a union official.

Rodney Janes, the United Auto Workers union chairman at the plant, told the Wall Street Journal that assemblers will need to work "excessive overtime" to account for the shortfall.

A Ford spokeswoman declined to confirm the parts issue, but said there has been strong demand for the new Super Duty trucks, which incorporate extensive alluminum body panels and a higher-strength frame.

"We continue ramping up production on the all-new Super Duty," said Kelli Felker, Ford's manufacturing and labor communications manager. "As with all vehicle launches, we are working closely with our suppliers to meet customer demand for the truck, which has been outstanding in its early weeks."

The move to aluminum on the Super Duty lineup will save about 350 pounds compared to as much as 750 pounds saved by moving the F-150 to aluminum. The 2017 F-250 through F-550 SuperCabs and SuperCrews will share cabs with the F-150 in a move that provides more interior room.