switched tires and have a problem

There is more to vibration caused by a wheel assembly than balance (you can balance a square wheel).

Lower profile tires will exagerate a vibration in terms of feeling it in the car. That same vibration might have been there but not as noticeable with your old tires (or you might have just gotten a lousy balance job). 95% of the public won't notice or care about a less than perfect balance so the sloppy techs get away with sloppy balance jobs.

I would see if you can find a shop with a Hunter GSP Series Tire Balancer. It has a roller that can measure uneven forces in the assembly that are not due to balance. The link below has a locator service.