steering column in a KW

This is exactly what mine is doing.. the faster I go, really anything over 55 and I'm asking for it.. Coasting down a long hill .. Forget it.. The only thing it will do is ride perfectly down the road.. So I - We have ruled out the allignment. They"my company" has checked it and we have had another driver drive it.. But not under the same conditions as out on a desolate interstate where you have to hold your own. Any thoughts?