Q&A

 Master

If the tire condition is OK and the balance is OK then the suspension needs to be checked for worn bushings, tie rod ends, ball joints etc. I would get a second opinion about the tires and rims, just to make sure they are not causing the problem. Sometimes rotating the tires will help to clear that up.
At what speed does this occur?

 Master

Before you do the wheel alignment have your tires balance this should solve your issue