Driveline vibration

Are you removing the bevel that the lug nuts center into when you drill to the 5/8 stud size? That bevel is important. It serves two purposes. First, it acts as a "lock" when the lug nuts tighten against it to keep the nuts from backing off. Secondly, it also helps center the wheel. If you remove all or most of the bevel when you enlarge the stud holes in the wheels, that could be the problem.