Syncro 16 Doka overloading caused driveshaft vibration

Hello All,
First of all, my apologies to those on multiple Forums & Lists for the crossposting.
For the past few years, I have been tossing various extra parts in the rear of my 1989 Syncro 16 Doublecab.
It seemed the natural thing since I only do not drive this Syncro often. I have others to drive. At some point,
the old 1.6TD engine and a pair of T3 (Vanagon) transaxles found a cozy spot in the cargo bed. There is a
fiberglass canopy in back so it made for perfect, reasonably dry storage. After a while there was a decided 
lean to the rear. It's no wonder since there was close to 1,000 lbs. (about 455 Kilos) of spare parts residing
in cargo bed.
In all this time, I notice that the truck had developed a vibration in between 100kph-120kph (62mph-75mph).
The vibration got so bad that the it was not comfortable to drive the truck faster than 100kph. Anyway, I thought
it might have been the cargo but leaned towards the idea that the driveshaft had just gone out of balance.
Well today, I decided to do some vehicle cleaning and emptied the contents of the Doka. The immediate effect
is the truck is now level instead of being about 3 inches low in the rear. I started driving home and felt the truck
definitely felt more balanced. The to my delight the annoying vibration had disappeared. I can only surmise that
overloading the rear caused the driveshaft to not line-up with the front differential, etc. The result of such misalign-
ment of the driveshaft has been discussed often on the (US/International) Syncro List.
The moral of the story is, if you have vibration at highway speeds, consider the attitude of your vehicle as a possible
cause. Overloading will do this temporarily. Worn or broken springs can contribute to this syndrone as well.