Stocks slumped out of the opening gate Monday despite the weekend's successful launch to the holiday shopping season. The Dow lagged 0.5%. The S&P 500 dipped 0.4% and the Nasdaq 0.1%. Volume was up 20% on the Nasdaq and 26% on the NYSE compared with the same time Friday. Some Internet retailers gained in early trade, with eBay (EBAY) and Liquidity Services (LQDT) each up 2%. Monday is