General Motors reported its second-quarter earnings, and it was a fairly weak performance. Car sales in the U.S. were up slightly last month, but they show the market is slowing down. Vehicles equipped with manual transmissions have accounted for 7 percent of sales so far this year, up from around 4 percent last year. All that and more, plus a look at the 2013 Chevy Camaro ZL1 Convertible.