In Slaton's first regular season game as a Texan, a 38-17 loss to the Pittsburgh Steelers, Slaton rushed 13 times for 43 yards and caught three passes for six yards. On September 21, 2008, Slaton scored his first touchdown in the NFL with a 6-yard run against the Tennessee Titans. He finished the game with 18 carries for 116 yards (6.4 average), including a 50-yard run, and 4 receptions for eight yards. Slaton totaled 104 yards in the first half alone, making him the second Texan ever to rush for 100 yards in the first half of a game, while his 50-yard run was the second-longest in franchise history. Following the performance, head coach Gary Kubiak named Slaton the starting running back. Slaton followed-up his first 100-yard rushing performance in his second start of his career, a 30-27 loss to Jacksonville, with 10 rushes for 33 yards and caught 8 passes for 83 yards, including a 30-yard touchdown reception from the wideout spot. Slaton finished the game with 116 total yards in his second career start. In Slaton's third career start, a 31-27 loss to the Indianapolis Colts, Slaton rushed for 93 yards and two touchdowns on 16 carries and also had a reception for three yards. Slaton's performance won him the NFL Rookie of the Week Award from NFLPlayers.com, and was nominated for the Diet Pepsi NFL Rookie of the Week Award for the third consecutive time, dating back to the Titans' game. In the following 29-28 victory over the Miami Dolphins, Slaton rushed 15 times for 58 yards and had a reception for 3 yards. In their consecutive victory against the Detroit Lions, Slaton totaled 80 yards and a touchdown on 17 carries and had three receptions for nine yards. In the 35-6 win over the Cincinnati Bengals, Slaton rushed 15 times for 53 yards with a touchdown. Slaton then had 12 rushes for 62 yards and 8 receptions for 56 yards in the 28-21 loss to the Minnesota Vikings. The game marked his second 100-yard all-purpose game of the season with a total of 118 yards.