Shares slipped at Tuesday's opening bell on nagging concerns that the stock market is overpriced after its 11-month run-up. The Nasdaq Composite Index <.IXIC> eased 6 points, or 0.31 percent, at 2,001. The Dow Jones industrial average <.DJI> shed 16 points, or 0.16 percent, at 10,592. The Standard & Poor's 500 Index <.SPX> fell 2 points, or 0.20 percent, to 1,138.|||