Jason Leffler made his Truck Series debut in 2002 and immediately became a contender for the series crown, posting eight Bud Pole Awards, 15 top-10 finishes and six runner-up efforts. While Leffler did not get a Craftsman Truck Series win, he averaged a top-10 finish and finished fourth in the series standings.
After single full seasons in the NASCAR Nationwide Series and Cup Series, which were marked by great speed, including tying a rookie record three Bud Poles in the Nationwide Series and his career first Cup Bud Pole in the inaugural event at Kansas Speedway, Leffler was not retained by Ganassi Racing following the 2001 season.
Coming into 2002, Leffler had only 65 stock car starts after a career in USAC. From 1997 to 1999, Leffler established himself as driver whose reputation was on a steep growth curve. He won three straight USAC national Midget championships, becoming the first driver in 37 years to accomplish that feat. Leffler also won the 1998 Silver Crown title in his first year in the series. In 1999, he won 11 races in a variety of USAC divisions and won four times in 2000 while beginning his Nationwide Series career.
Leffler was given a full-time Cup ride during the 2003 season pilot the NetZero Pontiac until Ward Burton took over the controls in October. Haas CNC Racing then expanded their partnership for 2004, with NetZero joining the team's new Nationwide Series program with Leffler as an associate sponsor for all 2004 events and primary sponsor of the effort for three races. Leffler was able to score his first NASCAR Nationwide Series win in his 56th start at Nashville Superspeedway that season.
For part of the 2005 Cup season, Leffler raced with Joe Gibbs Racing in the No. 11 FedEx Chevrolet.
Leffler completed his 2007 Nationwide series 3rd in final points standings, his best career finish to-date. He gained one win, seven top-five and 11 top-10 finishes, and two Bud Poles that season.
Leffler ran the 2008 Nationwide series driving the No. 38 Great Clips Toyota for owner, Todd Braun, alongside teammates Bill Elliott, Michael Waltrip, and Chad Blount. He finished 9th in points
Leffler finished 4th in points for the 2009 Nationwide series. This was his third consecutive season with a top 10 finish in points.
