Balancing issue?

I have a 1999 Oldsmobile Cutlass, 101550 miles, 3.1. I have had it into the repair shop 2 times within the past week, because when I am on the highway and have it going above 65 mph the steering wheel starts to shake really badly. The service dept. Balanced the front wheels, the first time it was fine for three days (even driving it on the expressway) then the next time I drove it, it was doing the exact same thing. I took it back to the repair shop they balanced the wheels again (supposedly a different way this time), once again it is behaving the exact same way. Anyone have any experience with this? Advice for the next step to take with it? The tires are not that old on it. So I wouldn't guess that that is the problem.