Slocum made his professional debut in 2002 with the Single-A Mahoning Valley Scrappers, going 5–2 with a 2.60 ERA in 11 starts.[5] In 2003, he spent the season with the Single-A Kinston Indians. In 22 games (21 starts), Slocum was 6–7 with a 4.46 ERA,[5] and he was named a Carolina League top prospect by Sportsticker. In 2004, he led the Carolina League in wins (15) with Kinston and tied for the league lead in complete games (2) and shutouts (2).[6] In November 2005, Cleveland added him to their 40-man roster.[7]
On April 21, 2006, Slocum was recalled from the Triple-A Buffalo Bisons.[8] He made his major league debut against the Kansas City Royals on April 22, pitching two innings, giving up two runs, walking two, and striking out two.[9] Slocum recorded a 7.71 ERA in four relief appearances before being sent back down to Buffalo on May 2.[10] He was recalled again on September 7 when the active rosters expanded.[11] In eight total appearances (two starts) with Cleveland, Slocum recorded an ERA of 5.60.[12]
Slocum began the 2007 season with the Bisons, but was limited to five starts due to injury, going 2–2 with a 4.15 ERA.[5][13] After recovering in the offseason, he was sent to Buffalo again to begin the 2008 season. Slocum was 3–4 with a 5.66 ERA in his first 11 starts before being recalled by Cleveland on June 4.[14] However, he did not feature in a game before being sent back down on June 8.[15] On July 4, Slocum was recalled again after transitioning into a relief role with Buffalo.[16] He was sent to the Bisons again on July 12 after struggling in two relief appearances.[17] On September 23, it was announced that Slocum would undergo season-ending elbow surgery.[18] He became a free agent after the season on November 3.[12]
Pittsburgh Pirates
On December 8, 2008, Slocum signed a minor league contract with the Pittsburgh Pirates organization.[19] After going 1–3 with two saves and a 3.94 ERA in 19 relief appearances with the Triple-A Indianapolis Indians,[5] Slocum was released on July 14, 2009.[12]