If you are feeling the vibration in the steering wheel, it may be the dreaded death wobble.
Usually happens around 55mph. If this is true, check all your front steering joints, knuckles & ball joints. Also check that the steering box & pitman arm are tight. If the steering stabilizer looks old, it probably is & replacing it cured my death wobble problems.
That said, do go ahead & check that other stuff first for safety's sake.