Tech led a sharp pullback in US stock futures on Tuesday as doubts about high-running valuations preyed on investors sifting through the latest flurry of quarterly earnings. S&P 500 futures (ES=F) sank 1%, while those on the tech-heavy Nasdaq 100 (NQ=F) tumbled 1.3%. Contracts on the Dow Jones Industrial Average (YM=F), which includes fewer tech stocks, fell roughly 0.7%, or around 300 points. Wall Street is getting nervous that companies aren't performing well enough to justify their high-riding market ...