With sport-utility vehicle sales surging, the Tesla Model X now outsells its showroom sibling, the Model S sedan, with 9,000 units delivered so far this year. March and June were its strongest months. This year’s tally is actually down slightly from 9,525 units delivered to customers during the first six months of 2018. Tesla’s federal tax credit being cut in half on January 1 probably didn’t do the Model X any favors.