To close out this question/ thread:
A dying coil/ bad spark will make ones car shake violently when the overdrive kicks in. Never would have figured that.
Got the opportunity to work on the car in 25deg weather-
and replaced the #5 coil. The spark plug (iridium) although loose, had good coloring to it so I left it in.
Car runs fine other than it has been mostly in storage 2 years so I have some rust on the brakes to work off. Just passed my NYS inspection
Not the best weather to be driving in, but figure I should run a few tanks of gas through it before putting it back in the barn.