McCumbee began his career racing go-karts at the age of ten. He has more than 100 victories in local, regional and national World Karting Association Dirt Series events, all which he accomplished in the five-year span from 1995–2000. He was also Allison Legacy Series National and Regional championship along with Rookie of the Year in his very first full season in the series in 2001. He also won the 2002 national title becoming the first and so far only two-time champion of the series. In 2003, he started late model racing at Myrtle Beach Speedway, and became the youngest rookie winner at the track.

McCumbee made his ARCA RE/MAX Series in 2004 at Michigan International Speedway for Hillenburg, but wrecked the #10 Fast Track Driving School Chevy after 21 laps and finished 37th. He finished fourth in the point standings in 2005, his first full year of competition, continuing to drive for Hillenburg, winning one pole and gathering ten top-ten finishes.

McCumbee moved to the NASCAR Craftsman Truck Series in 2006, initially as driver of the No. 06 Chevrolet Silverado for MRD Motorsports. After failing to qualify for the season opening event at Daytona International Speedway, he had two consecutive top-fifteen finishes before MRD closed, moving him to the No. 08 Green Light Racing Chevy owned by Bobby Dotter. He finished 9th in his first race with the team at Texas Motor Speedway, and split time in the next five races between Green Light's No. 07 and No. 08 entries with occasional sponsorship from U.S. Restoration, before moving to the No. 08 permanently with Garmin/The GPS Store as sponsor. He had two seventh-place finishes through the year and finished seventeenth in season points. During the season, he briefly was a member of Chevrolet's driver development program, but his contract was not renewed at the end of the season.

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