Finally,after much discussion on this and other forums,and after removing ventilation fans from under seats,I bit the bullet and paid local upholstery shop $400 to remove front seats and add 1" of the densest foam padding they had to the seats.Upon doing this,I discovered that the foam padding used by Toyota is really cheap stuff,with no resistance whatsoever.Problem solved now;and after recent 600 mile trip,it almost sits as good as my SL500.Girlfriend(not fat) said if it made her butt feel any better,we'd have to stop and address the situation,so I guess it was worth the money.Still think Toyota could have done better for that kind of money.Luck to the rest of you.