Hi,
I believe it is the U-Joints on your drive shaft that is causing it. I had a similar problem where it would vibrate between 35-45 mph acceleration and would go away after that. I replaced the all the U-joints (rt, center & left) even though only the left one was bad. Cost me around $100 for parts and $120 for labor. Hope this helps.
smk_texas
92 190e 92K