The old Xterras qualify as a "clunker," but the new Xterras don't qualify as the new fuel-efficient vehicle that you have to trade it in on. The "new" vehicle is required to have an mpg rating of at least 18mpg, the Xterra 4x4 only gets 17mpg. Not only that, but in order to qualify for the $4500 voucher your new SUV must get 5mpg better than the old.