(Reuters) - Fiat Chrysler Automobiles NV FCH.MI (FCAU.N) said on Thursday it would invest more than $1 billion in its Michigan plant and add 2,500 jobs as it benefits from the overhaul of the U.S. tax code. The company said it would spend the money to modernize the Warren Truck Assembly Plant in Michigan to produce its Ram Heavy Duty trucks. The company will relocate the truck’s production from its current location in Saltillo, Mexico, to the Michigan plant in 202O. The car maker also said it would make a special bonus payment of $2,000 to about 60,000 FCA hourly...