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.
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