Operators of some of the largest U.S. truck fleets, including Lowe’s Cos are accelerating a shift to natural gas fueled trucks, betting on new engine technology that promises to drop the cost of shifting from diesel fuel. Home-improvement retailer Lowe’s wants its delivery company to shift all of its several hundred trucks to natural gas by 2017. P&G already has 7% of its trucks on gas and could reach as much as 20% within two years. UPS says it plans to buy 1,000 natural gas trucks by the end of next year FEdex Corp plans to shift 30% of its long-distance trucks to natural gas over the next decade. The nation’s supply of relatively cheap natural gas is helping spur this shift. So are new natural gas engines that can power heavy-duty trucks that weigh up to 80,000 pounds. The first, a 12-liter Cummins Westport Inc. natural gas engine went on sale in July.