vibration at 60mph or above on 2005 Cadillac DeVille DTS

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 skill.car 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:
https://repairpal.com/directory?address=39170&car_brand_names=Cadillac