U.S. stock index futures were lower on Tuesday, indicating a modest retreat from the previous session’s rally, including the strongest session for the Dow in more than a month. * Energy shares will continue to be in focus as crude oil (CLc1) fell 2.3 percent to $47.58 per barrel, sending Exxon Mobil Corp (XOM.N) down 0.7 percent to $85 in premarket trading.