What is loose, the ball platform in the receiver hitch, or the ball in the ball platform?
You need to get a ball with a 1" or 1 1/4" shank, not the smaller 3/4". If you get the 1", then use the bushing that Toyota supplies with the ball platform. The hole in the Toyota ball platform is 1 1/4", for the larger 2 5/16" balls, and they supply a bushing for the smaller shank balls.
Also, I ran into problems using the Toyota bushing, as it is slightly longer than the thickness of the platform, and the nut bottomed out before the ball was tight in the platform. I had to take an angle grinder with a flap disk to it, and remove a 1/16" or so from the bushing.
--Mike