Thank you Guys. More food got thought.
I have tried switching tanks, electric fuel pump on and off. No change.
Oil pressure and temp are good and steady.
We took off MT governor and replaced it with PC?5000. Thought vibration was gone for about 6 hours, (hard to discern if turbulent), but now is returning. I am ignorant about the workings of a governor concerning oil pressure, linkage etc. Could I have an oil pump problem even though pressure to gauge is fine? Maybe looseness in the prop linkage? What about the counter balance weights in the prop itself?
I’m hoping it’s nothing too serious so that I can continue to chase the rabbit down the hole without a catastrophic event.