steering shakes

I have developed a shake in my steering wheel above 100 km. If I accelerate relatively quickly through 100 km to 140 km no shake is felt. As long as my foot is on the gas, no shake. When I accelerate slowly past 100 km, or back of the gas after 100 km to 140km the shake is felt. I've balanced the wheels three times at different shops with no help. I am thinking about changing bushings and replacing the shocks. does anybody have possible solutions for this problem?:(