He ran only part-time in 2003 as Roush moved him up to a full-time ride in the Winston Cup Series for that season, but he returned to contend for the Busch Series championship again in 2004. He placed third in the standings behind Martin Truex Jr. and Kyle Busch. From 2005 to 2009, Biffle raced part-time for Roush Fenway Racing in the Busch (now Xfinity Series) every year.