Addington worked as
Jason Keller's crew chief in the Busch Series, and the combination collected ten wins. Bliss also part-time in the Cup Series for JGR in a fourth car for the team, the No. 80, and Addington was also his crew chief in that series. In 2005, Addington became the crew chief for Joe Gibbs Racing's No. 18 car in the NASCAR Cup Series driven by
Bobby Labonte, replacing Michael "Fatback" McSwain. JGR also switched from Chevrolet to Toyota that year. Busch lead the points with eight wins going into the
Chase for the Cup. The team had numerous problems as soon as the Chase started, such as engine failures and wrecks, and Busch finished tenth in the twelve drivers in the Chase. Busch ended the season with 21 victories in NASCAR's big three divisions (Sprint Cup, Nationwide, and
Craftsman Truck Series), which was seven more wins that any driver had made since the Craftsman Truck Series began in 1995. which was driven by
Austin Dillon as Stewart had been injured in a dirt racing crash before the race at Watkins Glen which sidelined him for the rest of the season. Addington was relieved of his duties as crew chief of the No. 14 on November 19, 2013. On November 21, 2013, it was announced that Addington would join
HScott Motorsports in 2014 as the crew chief of their No. 51 car, driven by
Justin Allgaier, as well as the team's competition director. In 2016, Allgaier went back to the Xfinity Series was replaced by
Clint Bowyer and the car was renumbered to the No. 15. In 2016, HScott Motorsports closed down after the end of the season, leaving Addington a free agent. He remained without a crew chiefing job for five years. In 2022, Addington returned to NASCAR and became the crew chief for the No. 38 car for
RSS Racing in the Xfinity Series driven by
C. J. McLaughlin and
Parker Retzlaff. In 2023, he returned to crew chief the RSS No. 38 car, primarily driven by
Joe Graf Jr. For the season-opener at Daytona, Graf Jr. and
Ryan Sieg switched rides with Sieg driving the No. 38 and Graf driving the No. 39, with Addington crew chiefing Sieg in that race. For the next two races at Fontana and Las Vegas, Graf drove the No. 19 car for
Joe Gibbs Racing instead with
Kyle Sieg, Ryan's brother, moving from RSS's No. 28 car to the No. 38 and
Alex Labbé driving the No. 28. Addington and Brad Parrott, normally the crew chief of the No. 28 car, switched cars for these races with Addington crew chiefing the No. 28 driven by Labbé and Parrott crew chiefing the No. 38 driven by Kyle Sieg. ==Personal life==