AWWW, The dreaded 60-65 mph shimmy...It SUCKS!!!! I've battled with this problem on many a lexus' And what i've found is the following: A quality tire is a must. I've had brand new tires that rode like sh*t all b/c i "tried " to save some money. Second, is the SAME shop doing the balance job for you? Generally speaking monkey see, monkey do meaning the machine is only as good as the person using it...If you really want a perfect balance job find a place that that has a "road force" balancer. Any reputible custom rim shop should have one...Hope this helps!
P.s. You may also want to have your tie rods checked. Just a thought