In 2003, Miller ran four
NASCAR Grand National Division, West Series races, finishing in the top ten twice. He made his major league NASCAR debut at Mesa Marin in the
NASCAR Craftsman Truck Series, finishing eighth in the No. 6
Chevrolet Silverado owned by
Kevin Harvick Incorporated. He ran three more Truck races that season in the No. 68 truck owned by his father; his best finish was 14th at
Las Vegas Motor Speedway. The following season he ran another Truck Series race in the No. 2
Team ASE Racing Dodge Ram for
Ultra Motorsports at Las Vegas, finishing 20th, as well as making his Busch Series debut with Richard Childress' No. 29 team at
Kansas Speedway, where he finished sixteenth. In
2005, Miller was hired to drive the No. 21
Reese's Chevrolet Monte Carlo in the Busch Series for twelve races, sharing the ride with
Kevin Harvick. Miller posted two top-ten finishes over the course of the season and finished 48th in the final standings. Harvick's decision to run the full Busch schedule in
2006 forced Miller out of a permanent position with RCR. He remained with the team as a fabricator and test driver, occasionally practicing and qualifying race cars for the team as necessary. He spent
2007 driving the No. 40 Westerman Companies Chevrolet for Curtis Key. Miller made his first attempt at a NASCAR race since 2007 when he piloted the No. 14
Chevrolet for
NTS Motorsports at
Texas Motor Speedway in the
Camping World Truck Series on June 8, 2012. ==Motorsports career results==