In 2004, Hamlin competed in five NASCAR Craftsman Truck Series (NCTS) races with EJP Racing, and had a tenth-place finish in his NASCAR debut at Indianapolis Raceway Park. He later ran his first career ARCA RE/MAX Series race at Talladega Superspeedway, finishing third in the #10 Pontiac owned by Andy Hillenburg.
His final start of the year came at Darlington Raceway, when he made his Busch Series debut.
BRP-Powertrain has introduced a single (engine) brand race series for the MAX engine concept - called Rotax Max Challenge. This race series is organized in various classes (125 Micro MAX, 125 Mini MAX, 125 Junior MAX, 125 MAX and 125 MAX DD2) in around 60 countries.
Competitors from the national Rotax Max Challenges in the 125 Junior MAX, 125 MAX and 125 MAX DD2 class can qualify to participate at the annual Grand Finals of the Rotax Max Challenge, where most of the costs are covered by BRP-Powertrain.
Hamlin ran the full season in 2005 after he replaced Mike Bliss in the #20 Rockwell Automation Chevrolet in the Busch Series. He ended up finishing 5th in the final championship points standings as a rookie in that series, with 11 top 10's and earnings of $1,064,110.00.
Hamlin also ran his first Nextel Cup Series races in 2005, making his Cup debut at Kansas Speedway as driver of the #11 FedEx Chevrolet for the 2006 season, after Jason Leffler was released, and made seven starts in the Cup series in 2005.
He finished the Cup season with three top 10 finishes in those seven starts and one pole at Phoenix International Raceway.
His performance in 2005 was impressive, as Leffler had performed embarrassingly in the same car earlier in the season.