General Motors' Chevrolet Camaro sales are dropping as buyers shift to the newer 2015 Ford Mustang. Chevrolet will introduce an all-new 2016 Camaro in the next model year that should boost sales. Power to the Dodge Challenger was beefed up for the 2015 model year, which helped lift sales, but the Challenger remains in third place in sales volume among the trinity of American muscle cars.