[Half-Inch Stud]

Sure, all of the above.

Flywheel/pressure plate/fork/throwout is the likely culprit.

Then I'd figure on the sausage driveshaft if you say it vibes on the highway.

Engine power balance is possible if would also note an occasional exhaust burp or backfire in front of the mufflers....happened to me. A brand new shorted sparkplug (properly gapped) caused a dead cylinder.

Good luck.

H.I.