I dunno, Had a cuda long ago that was doing same kindof thing at 135 mph on a straight road. It was still gaining speed, and as soon as it started lifting up then settling down, then up again, it was time to lift. After slowing it back to about 85, which felt like 30, I was figuring the car was trying to get on top of air underneath it. Make sense? That was stock suspension, and I was glad to not have to turn the thing at that speed.