Pickups, for years, have been the best-selling vehicle in the United States. But recently released year-to-date sales are showing that overall, pickup truck sales have fallen this year. Sales for the Nissan Titan have dropped more than 9% this year. In September of 2006, more than 6,000 Titans were sold. This past September, sales barely beat the 5,000 mark. Chevrolet’s…