COLLEGE STATION, Texas — Marcel Reed threw for a career-high 439 yards and three touchdowns and No. 3 Texas A&M rallied from a 27-point deficit to remain undefeated with a 31-30 victory over South Carolina on Saturday.It’s the biggest comeback in school history, eclipsing a 21-point rally by a Johnny Manziel-led team in a 52-48 win in the 2013 Chick-Fil-A Bowl over Duke. Entering Saturday, teams were 0-286 in Southeastern Conference play since 2004 when trailing by 27 points or more.Reed bounced back from an awful first half where he was intercepted twice and had a fumble returned for a score to put the Aggies in a 30-3 hole with a dazzling second half to keep Texas A&M (10-0, 7-0, No. 3 CFP) on track for its first trip to the College Football Playoff.The Aggies took the lead for the first time on a 4-yard run by EJ Smith with about 11 minutes left.Texas A&M had a first down at the 1 after that, but Jamarion Morrow fumbled on a trick play and the Gamecocks recovered with about three minutes to go.Dalton Brooks and Cashius Howell sacked LaNorris Sellers on consecutive plays to bring up fourth-and-16 with about 90 seconds to go. Sellers scrambled on fourth down and he was stopped short of the first down marker to seal the victory.Sellers threw for 246 yards with two touchdowns and an interception for South Carolina (3-7, 1-7), which lost a fifth straight game.Izaiah Williams caught a 27-yard TD pass from Reed to make it 30-10 on A&M’s first drive of the second half. Reed had a 16-yard run on fourth-and-12 to keep the drive alive.Reed found Ashton Bethel-Roman for a 39-yard TD to get the Aggies …