I agree with Peter on the suspension noise and would really look closely at the trans mount from your description of the noise at speed.
Most driveshft vibrations are worse at low speeds and high loads.
I am giving that advise because I am trying to be civil fisrt before I go ballistic:
"which I'm now not-so-affectionately calling "Money Pit"."
This has to be the most amazing tale I have ever read. A non technical, out of funds person, buys a 25 year old car 1500 miles away on ebay as a daily driver.
Am I supposed to feel sympathetic since you are now not affectionate to this characature called a "money pit"
Just how can anyone with any intelligence buy an antique automobile at distance and expect to have no costs and use it as daily transportation.
Don't blame the GD CAR! And don't blame ebay!
Bosch Master, ASE Master, L1
33 years MB technician