First, second and third reson for steering wheel shaking at higher speed is improperly balanced tires. Anything else will be 4 th reason. My own experience. I had the same issue with my 2016 model monterosport. I balanced and aligned my tires from 2-3 shops and the problem was persisting. Mitsubishi team checked thoroughly for any issues with steering and related parts and they didnt find anything. They suggested to do balancing from their own main workshop at muscat. I took my car to their workshop, got it done and thus my steering shake has totally disappeared.