Mowlem also finished second in the GT class in the Rolex 24 at Daytona in 1999. That same year, Mowlem and with co-driver David Murry competed in the GT class in the ALMS finished first in the GT class at Laguna Seca Raceway, setting the fastest GT lap of the race with a new track record. The 2000 season included second place class finishes in the 12 Hours of Sebring and the 24 Hours of Le Mans. By then Mowlem was a full-time competitor in the North American-based ALMS while living in the UK. In 2001, Mowlem continued his ALMS career. He drove with a number of co-drivers in the GT and GT1 class. At Sebring, Mowlem was teamed with Petersen Motorsports but the team withdrew the car following the death of co-driver Bob Wollek following a non-racing incident in the Sebring area. Mowlem posted the fastest lap by a GT1 car during the Le Mans race.