Car companies delivered a solid September. Detroit's Big Three automakers -- General Motors (GM), Ford (F) and Fiat Chrysler (FCAU) -- each reported double-digit percentage increases over the month. Sales were boosted by cheaper gas, a stronger economy and a later Labor Day weekend that made year-ago comparisons favorable. Stocks were modestly lower, though trading remained cautious ahead of Friday's release of the nonfarm payrolls report. The latest check on the manufacturing sector in the U.S. showed activity teetering near contraction. The measure showed growth at its slowest pace in more than two years as a stronger dollar and weaker global demand stunted exports.