Is it felt through steering wheel? Could be a simple wheel balancing issue.

If felt through the seat could point to rear wheels out of balance/buckled wheel/out of shape rear tyre.

Clunk could be from engine mountings.

Usually if it's a driveshaft inner cv joint problem, you'd get a vibration under hard acceleration in lower gears as well as higher speeds.

Not experience a throttle sticking problem on Focus diesels before,not sure what to suggest there.