I believe I got it in August or September 2009, because it was soon after Snow Leopard was released and it’s the 21.5" version, the cheapest one and I have upgraded it with extra RAM. (It’s in the studio, so I can’t check all the details now.)
I had the same experience as you. The new driver alone didn’t change anything, but after upgrading the OS from 10.8.x to 10.9.1 the problem was solved.
I don’t know if it will work for you and solve you problems, but it certainly solved my problems. 