Due to the injury as well as an unstable financial situation at Petree Racing, Hamilton left the Winston Cup Series for the Truck Series driving for his own team, taking the Square D sponsorship with him. Driving the No. 4 Dana Dodge Ram Hamilton picked up two wins in his first year on the circuit and finished sixth in points. The following season, he picked up four wins and clinched the championship, marking the first time since Alan Kulwicki's championship in 1992 that an owner-driver won a NASCAR championship. He switched to the No. 04 in 2005.