AJ Allmendinger took the step up to the Champ Car World Series in 2004, with the same RuSPORT team with which he won the 2003 Toyota Atlantic Championship.
In his first season on the circuit, he finished five of the season's last six races in the top six, capped by a third place run in the season finale. He earned the Roshfrans Rookie-of-the-Year award by a 41-point margin, becoming the first American-born driver to claim the honor since 1991.
In 2005, he finished fifth in the championship standings on the strength of six top-fives and nine top-10s.
The following year was a breakout campaign for Allmendinger, but the young American driver had to endure quite a bit of adversity before making his mark.
After the first four races of the 2006 Champ Car season, the Los Gatos, Calif. native was released by RuSPORT. Just a few days later, he signed with Forsythe Championship Racing. With his new team, he recorded three consecutive victories and finished the year with five victories overall. Also that season, Allmendinger got to taste NASCAR Camping World Truck Series action - racing three times with Bill Davis Racing, scoring a best finish of fifth in the John Deere 250 at Talladega Superspeedway.
Both his open wheel and Truck Series results led the newly established Red Bull Racing team to offer him a NASCAR Cup Series ride for the 2007 campaign, where he teamed up with Red Bull driver, Brian Vickers.
In his first season driving in the Cup series, Allmendinger finished 44th, driving 17 of the 36 races. He led one lap during the season and earned $1,263,263.
2007 was also Allmendinger's debut season in the Nationwide Series, where he drove in seven of the 35 Nationwide events, gaining a 59th place finish in final standings. Perhaps Allmendinger's 2007 truck campaign was a bit more successful than his Nationwide run as he finished 34th (career best to-date) in final points and gained one top-five and two top-10 finishes, completing his run for the season at New Hampshire on September 15.
In 2008, Allmendinger qualified for 27 Sprint Cup races and scored his first top-10 finish of his career (10th at Indianapolis). But his time with Red Bull came to an end before the season was over and Allmendinger bounced around to Michael Waltrip Racing and Gillett Evernham Motorsports as the season ended. With GEM's merger with Richard Petty, Allmendinger will get a chance to drive the No. 44 Dodge to start the season.