The Dow Jones Industrial Average (^DJI -0.13%) is having a strong year. The venerable market index of 30 bellwether stocks is up more than 15% on the year. It's on track for a better performance than last year, when it delivered a nearly 14% return. Several stocks contributed to the strong run of the Dow Jones this year. Here's a closer look at the top five performers: Dow Jones StockYear-to-Date ReturnWalmart (WMT -0.20%)60.3%Goldman Sachs (GS -0.94%)53.9%American Express (AXP -0.46%)53.1%JPMorgan (JPM -0. ...