A quick history, my car already had the increasing vibration at speeds over 75. Car is an M6

I was moving the last of my stuff out of my old place and I had approx. 150 - 200 lbs of crap in my car. Most of it was in the rear with the heaviest stuff on the back of the fold down rear seat.

When I started to get up to speed I noticed that I had about double the vibrations I usally do.

I haven't felt this when I have had a 150 - 200 lbs passenger in the car. I feel most of the vibrations in the stearing wheel and towards the back. Almost like my subframe is trying to walk out on me.

Could this be an indicator of rear shocks/springs heading south, or just the fact that I already had a vibration problem and the extra weight in the wrong area amplified it?

Luckly my new place is 1.6 miles round trip from my work, but I am about to make a road trip with all the same stuff in the car. Sorry for the long post.

Any Ideas?

How new is your clutch? Your flywheel might need to eb resurfaced

You might want to check or replace your u-joints. You have a lot of driveline speed with 4.10s. Adding weight changes the angle of the driveshaft toward the rear end. That could make a marginal u-joint feel worse.

Ditto that.

could it be bent drive shaft bent ackles or the splines could be bent