Lamar began racing go-karts at the age of 5, and won a total of twenty-five track championships and three International Karting Federation Regional titles. At the age of sixteen, Lamar started racing stock cars at Stockton 99 Speedway and finished eleventh in points. Over the next three years, he raced on many West Coast short tracks, and won the Shell Oil Tri-Track championship.

In the year 2000, Lamar began racing in the USAC Western States Sprint Car Series. He posted seven top-fives and finished third in points, winning Rookie of the Year. The following year, he joined the NASCAR AutoZone Elite Division Southwest Series, and would win Rookie of The Year that year as well. He would go on to win two races and finish second in points in 2002 as well.

Lamar signed with Kevin Harvick Incorporated in 2005, competing in a limited number of NASCAR Busch Series, Craftsman Truck Series, and NASCAR Grand National Division, West Series races. In addition to two victories in the West Series, Lamar also won the Copper World Classic at Phoenix International Raceway that season. In the Truck Series, he raced the #92 Chevrolet Silverado twice with a best finish of 21st. He qualified 8th in his Busch Series debut in the #33 Chevrolet, but wrecked early in that race and finished 41st. He would begin racing in the Busch Series full-time in 2006 in the #77 Chevrolet, and began the season with a second-place finish at Daytona International Speedway. After two additional top-tens in the first third of the season, Lamar's results began to fall off, and was removed from the ride late in the season at the request of Dollar General, who wanted NEXTEL Cup drivers in the car.

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