U.S. factory output slumped 0.5% in September, as a strike at General Motors caused a steep decline in auto production amid broader struggles for manufacturers. The Federal Reserve said Tuesday that manufacturing production has fallen 0.9% over the past 12 months, a reflection of the disruptions and uncertainties caused by the U.S.-China trade war. The figures showed some stability, however, as factory output increased during the recently ended third quarter after having declined for the first six months of the year.