Driving for Steve McGowen in 2009, Mayhew scored his first win in the series at Iowa Speedway, finishing the season sixth in points with two wins; despite only scoring one win in 2010, he finished second in points.[3] In 2010 Mayhew also made his debut in the NASCAR Camping World Truck Series, driving Kevin Harvick Incorporated equipment operated by McGowen; he ran a limited schedule in the series in that year and in 2011, winning a pole at Iowa Speedway in the latter year.[5] Two of Mayhew's 2011 races were driven for KHI itself; in both races he finished third, his best career finish in the series.[6] He also competed in one Nationwide Series race for KHI in 2011,[6] finishing 10th in his first start in the series.[7] Also in 2011, Mayhew qualified the No. 66 HP Racing Toyota for the Sprint Cup Series' Toyota/Save Mart 350 in place of regular driver Michael McDowell, who drove the car in the race.[8][9]
Returning to the K&N Pro Series West in 2012 after running a limited schedule in the series in 2011,[2] Mayhew led all 50 laps of the opening race of the 2012 season at Phoenix International Raceway.[10] He scored top 10 finishes in each of the season's first seven races; in June, he was signed by Phil Parsons Racing to race the No. 98 Sprint Cup car in the 2012 Toyota/Save Mart 350 at Infineon Raceway;[11] Mayhew finished 40th in the event.
Mayhew was also asked by Kevin Harvick to stand by as a substitute driver during the summer of 2012, on call to replace Harvick in the No. 29 Chevrolet if needed as Harvick and wife DeLana expected their first child.[12] In the fall of the year he competed for Brad Keselowski Racing in four races in the Camping World Truck Series.[13]
^ ab"David Mayhew". NASCAR Home Tracks. Turner Sports. Archived from the original on 2012-06-26. Retrieved 2012-03-04.
^ abGriffith, Mike (August 3, 2011). "Opportunity knocks for Mayhew". The Bakersfield Californian. Bakersfield, California. Archived from the original on 2020-01-10. Retrieved 2012-03-04.
^Barber, Phil (June 26, 2011). "Gordon makes amends". The Press Democrat. Santa Rosa, California: Santa Rosa, California. Archived from the original on September 12, 2012. Retrieved 2012-03-04.