vibration at 60mph or above on 2005 Cadillac DeVille DTS

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
vib. at 60mph+ .have tied new tires, new rims, balance, alignment. local cad. dealer no help.he can't find obvious reason, but question mechanics training and has 150,000 miles-has been maintained with care.
(1) Answer
Find a Caddy or GM specialist. An alignment or tire shop may be able to help you.
If you want to find a specialist, here's a directory link for you: