Need some help here - 2008 GT500

Some background...: If you view my other posts, i had a 07 gt and was going to do a 5.4l swap. Well, i figured it was too much of a waist of time and just bought a 08 performance white gt500.

I bought this gt500 on wednesday and it came with some really ugly Cragers. I bought some chrome fr500 wheels from american muscle to replace those and bought new tires as well. Wednesday night i put the new fr500s on and was so happy with the way they looked. I took it for a drive the next morning to see how they road and the steering wheel shook like crazy at 60mph. I figured it was a loose lug and went home and tightened them all. Took it out for a drive again to make sure it was fixed, and it wasnt. So then i re-balanced all of the wheels, and then took it out AGAIN and it did it AGAIN.

Then, i checked to make sure there were no washers over the studs that were ment for the stock wheels and there wasnt. I went back to the lug nuts that came with the car to see if thatd fix it. Nothing has fixed this and its getting very annoying.

any help?