General Motors ( GM) said Tuesday that November auto sales dropped 18% from a year ago, a time when industry sales were boosted by zero-percent financing. It also set a succession plan for its outgoing CEO. The Detroit-based company said total sales fell to 309,263 vehicles from 363,721 in the year-ago period. GM said car sales fell 6% to 137,401 units, while truck sales plunged 26% to 171,862 units. GM also raised production estimates for its North American factories in the fourth quarter by 5,000 vehicles, bringing the total to about 1.42 million cars and trucks. For the first quarter of 2003, GM plans to produce 1.4 million vehicles, up from the previous estimate of 1.35 million. GM also said Rick Wagoner will relinquish his role as chief executive to become chairman when Jack Smith steps down in May. Smith announced earlier this year that he would retire in 2003, when he turns 65. He was named CEO in November 1992 and chairman in 1996. The Dow component's shares dropped $2.05, or 5.1%, to $37.90 on the Big Board.