Could be alignment?
If you've curbed a wheel while parking, or even if you just hit one entering a driveway, you could have thrown it out of alignment. Did this with my Miata a couple years back and it felt like I was going to fly off the road whenever I got above 65.
get a friend to follow you from behind. use at least a 2 lane (one way..and preferably one with a high speed limit) highway so that he can look at your car from both sides while driving. check and see if he can visibly see any warping (bent rim movement). you can usually catch these things with your eye. if this does not work...
get an alignment. this is probably where your problem is at. (you do the friend thing first, obviously, because its free) this is assuming of course that your rotation and balancing were done correctly.