1996 E320 shaking when driving

I have gone through 4 sets of tires, had many alignments, and the tires have been balanced time and again. After the factory tires were taken off and a new set from same manufacturer were installed, the vehicle starting shaking at aroudn 50-60mph. After 4 sets of tires, it is still ongoing. This also was happening to my 1985 190E, but not to the extreme that I have with the E320. Mercedes has looked at it over the years and claims there is still nothing worn out. I have 96K miles on it right now, no leaks, no electrical problems. The car is in fantastic shape with the exception of the shaking. I have also had a OEM screw set in the front so it is in better permanent alignment according to the shop that installed it. Shakes worse then before.