Your freeway issue sounds like worn steering components. They're fairly cheap, I think I paid around $250 for 2 tie rod assy, center/drag link, and idler arm. Get the Lemfoerder parts, the cheapo's aren't worth it.
Could also be thrust arms, ball joints, etc. Lots of components can make them unstable. Might be worth a few bucks to have it checked out, then at least you'll know what has to be replaced, and whether or not you can do it yourself.
ASC would not be related to this.