Japanese automakers are taking on Detroit’s Big Three and scrambling to expand their share of pickup truck sales in the United States, as record low gasoline prices curb demand for their once best-selling small and medium-sized sedans. Soaring demand for SUVs and pickup trucks drove U.S. auto sales to a record high last year, as the lowest fuel prices in seven years prompted a shift from sedans and smaller cars to larger vehicles in the world’s biggest auto market. The big U.S.