My 98 e320 is shaking in the highway. I can feel the slight shake at low mph, but when i get going 60 or more the car will shake when i take my foot off the gas or when I am barely pushing the gas. IT also shakes, but less, when I am accelerating. When I put the car into neutral at these speeds, the car shakes even more. I am hoping that the tires need to be balanced. Any ideas?

__________________
1998 E320 150,000
1980 300SD 240,000
1965 190D 79,000