Thanks all for your replies. The tires and wheels are stock (I only have 4800 miles). I think the guy on the Road Force Balancer is trained. Hard to verify that but they've been at for a few years so likely they have overcome the typical errors.
Fourthlexus - that's a scary story. This is my 3rd one; One 2004 ES for my wife (still has it - great car), one 2004 RX for me ( I traded it for the LS), and now the LS. Never had a problem before now. I'm cringing at the prospect of dealing with this for months on end after spending that kind of money.
In the absence of others weighing in with simiilar stories and similar resolution, I think I will continue to focus on the tires. I thoough I might learn from others about a drive train problem, trans issue, dampers etc, b ut no such revelations as of yet.
I appreciate all the ideas and I will continue to probe ... Ughhhh,,,,I'd rather be driving and not thinking about it.