Stocks added to gains after Federal Reserve Chair Janet Yellen made the case for another rate hike. Yellen's confidence in the U.S. economy soothed investors' fears over earlier data that showed weaker growth over the second quarter. In a widely anticipated speech at Jackson Hole, Yellen said the U.S. economy has strengthened in recent months to the point where another rate hike should soon be warranted. Yellen expects moderate growth in GDP over the next few years. Consumer sentiment dipped in August in the final reading from the University of Michigan. Views over personal finances turned weaker, even as expectations over economic growth improved. GameStop (GME) - Get Report slipped as quarterly sales missed estimates. The video-game retailer's same-store sales fell more than 10%, far worse than an expected decline no more than seven percent.