Lieb returned to the FIA GT Championship where he won the GT2 Drivers title with Mike Rockenfeller for GruppeM Racing, netting a class win at the Spa 24 Hours along the way. He also raced in the Le Mans Endurance Series, winning three of four races and the championship with Sebah Automotive. Lieb also won the GT2 class at the 24 Hours of Le Mans with Mike Rockenfeller and Leo Hindrey. In 2006, he won the Le Mans Series GT2 championship with Joël Camathias, driving for Autorlando Sport. In 2007 and 2008 Lieb drive for Team Felbermayr-Proton in the Le Mans Series with a Porsche 911 GT3-RSR (2008). In 2009, Lieb teaming up with Richard Lietz in the Porsche 911 of Felbermayr Proton in the European Le Mans Series. He won the GT2 class championship with three wins in five rounds. On his return to the 24 Hours of Le Mans, who ran for Felbermayr-Proton alongside Lietz and Henzler, had to retire. He also disputed the round of Zolder for the FIA GT Championship for Prospeed, which finished 8th with Darryl O'Young. Instead, he earned his third victory in the 24 Hours Nürburgring for Manthey. In the American Le Mans Series, was 4th in Sebring and 5th Petit Le Mans as third driver of Bergmeister and Patrick Long Flying Lizard, and came 2nd at the time of Miller with Henzler for Farnbacher-Loles' team, always in a Porsche 911 GT2 class. Lieb and Lietz successfully defended the drivers and teams titles of GT2 class in the 2010 Le Mans Series, with three wins against two semiofficials' Ferrari F430 of AF Corse. Also, he earned his second victory in the GT2 class at the 24 Hours of Le Mans, once again alongside Lietz and Henzler in the Porsche 911 Felbermayr-Proton. Lieb returned with Bergmeister and Long for Flying Lizard in the two main races of the American Le Mans Series: Sebring finished 4th and 5th at Petit Le Mans. Returned to the 24 Hours of Spa as Prospeed driver, accompanying Marc Goossens, Marco Holzer and Westbrook in a Porsche 911 GT2 class, in this occasion the principal during the race, but abandoned. Lieb continued contesting the European Le Mans Series in 2011 for the Felbermayr-Proton team. He and Lietz managed two podiums but neither wins in five rounds, so that finished 5th in the drivers' championship and 3rd in the teams championship