Drivers fuel up at a Costco gas station in Roseville, Mich. Paul Sancya/AP hide caption toggle caption Paul Sancya/AP Stay up to date with our Up First newsletter sent every weekday morning. In the hunt for cheaper gas, people are going out of their way for discounted fuel at Costco and Walmart — many of them visiting for the first time. Drivers also are now filling up more often, but topping up with fewer gallons at a time. As the U.S. war in Iran continues to drive up gas prices, Costco's gas stations have been selling record amounts of fuel, executives told investors on a call Thursday. In fact, Costco had never sold as much gas as it did between April and mid-May, CEO Ron Vachris said , with stations having to get multiple daily gas deliveries to keep up. People have been willing to drive further and wait in line longer to buy cheaper gas.…