GM names new head of North American manufacturing DETROIT (Reuters) - General Motors Co (GM.N) on Monday named a new head for its North American manufacturing, replacing an executive who last week was assigned to cut waste at the U.S. automaker. Gerald Johnson was named vice president for North American manufacturing, effective July 1. He will be responsible for 74,000 employees at 56 plants, and will report to global manufacturing chief Tim Lee. Johnson, a 33-year GM veteran, was most recently executive director of global program quality and launch. On June 10, GM said Diana Tremblay, the current North American manufacturing chief, would assume the newly created role of global business services vice president and report to Chief Financial Officer Dan Ammann. She will focus on simplifying back-office processes and systems to improve speed and cut costs. The switch comes at a critical time for GM, which has started selling the new 2014 Chevrolet Silverado and GMC Sierra full-size pickup trucks, vehicles that Citigroup Global Markets has estimated could generate an additional $1 billion in operating earnings in 2013 and 2014. The manufacturing rollout will continue through this year and into next as GM introduces different models of its highly profitable big trucks and companion full-size SUVs. Reporting by Ben Klayman in Detroit; editing by Jim Marshall