4:77's & 35's...some stats...

[Ldub]

Your driveshaft and universal rotation is now faster at 55 (not that you didn't know this) so was there vibe before at 65???

Yep.
Also, I re indexed the drive shaft/third member connection 180 deg, on the chance that it would help, but alas, not so much...

The funny part of that is:
I had backed into my parking spot (on a slight incline) & was about to proceed with the "laying on of the wrenches", when Marlins experience flashed into my brain.
I then pressed the wheel chocks into service...

[Ebenezr]

Yep.
Also, I re indexed the drive shaft/third member connection 180 deg, on the chance that it would help, but alas, not so much...

The funny part of that is:
I had backed into my parking spot (on a slight incline) & was about to proceed with the "laying on of the wrenches", when Marlins experience flashed into my brain.
I then pressed the wheel chocks into service...

YES understood. You do not want to be a human wheel chock. but U joints are noted for singing at 55 MPH.