DETROIT—General Motors is shutting down its pickup truck factory in Ft. Wayne, Indiana, for two weeks next month because the company has run short of computer chips. The auto industry is still facing supply chain issues more than a year after a global chip shortage first emerged in late 2020. Chip supplies have improved during the first three months of this year compared with 2021, GM said, improving production and deliveries in the first quarter. But there’s still uncertainty in getting supplies from chip manufacturers. The Ft. Wayne plant will be closed the weeks of April 4 and 11. It has been running on three shifts per day making Chevrolet Silverados and GMC Sierra light duty pickups. The plant employs more than 4,000 blue collar workers.