Well, I've let this thread sit for quite a while since my wife has been driving the car. After getting behind the wheel a bit again, I'm motivated to get this fixed. Any chance that worn motor mounts could be the cause of my woes?

Motor mounts, transmission mount, pitch mount, any of those being worn will transfer excessive vibration to the chassis of the car.

 

Is this a shaking feeling or is it a buzz vibration?

Definitely more of a shaking vibration. Any thoughts on which of those mounts to look at first?

Test compression.

I repeat, vacume gauge?

 

Do that before a compression test it will tell you where to look.

You can check all of them. That's probably not the cause of your shake though.