Falloff in F-Series is trouble for Ford.

Just four months ago, Ford Motor Co. confidently reported that its Way Forward turnaround plan was on track, an assertion made easier with the F-Series pickup truck serving as a reliable powerhouse to carry Ford through a challenging year. Mark Fields, the automaker's president of the Americas, stood before a crowd at the New York International Auto Show at the time, boasting of the company's F-Series leadership and dismissing critics who wondered whether the momentum could continue.