DETROIT—The global shortage of computer chips is getting worse, forcing automakers to temporarily close factories including those that build popular pickup trucks. General Motors announced Thursday that it would pause production at eight North American plants during the next two weeks, including two that make the company’s top-selling Chevrolet Silverado pickup. Ford will stop making pickups at its Kansas City Assembly Plant for the next two weeks. Shifts will be cut at two more truck plants in Dearborn, Michigan, and Louisville, Kentucky. The cuts will compound an already short supply of cars, trucks, and SUVs on dealer lots nationwide that have pushed prices to record levels. Automakers reported that U.S. dealers had just under a million new vehicles on their lots in August, 72 percent lower than the 3.58 million in August of 2019. “It now appears to be accelerating in the wrong direction,” said Jeff Schuster, president of global …