A glut of inventory is prompting General Motors Co. to reduce production at its Detroit-Hamtramck Assembly Plant, as well as at factories in Lansing, Ohio and Kentucky. GM says it had more than 874,000 cars, trucks and crossovers in its inventory at the end of November — the most it has had in its U.S. stock in eight years, when vehicles went unsold during the Great Recession. And with some car models nearing six months of supply, GM will stop assembly lines for three weeks in January at Detroit-Hamtramck, according to the United Auto Workers union.