I am having this issue with TB on my Win8 64b laptop. (Laptop has Intel Core i7-4710HQ, 8GB RAM, TB running on SSD and dedicated graphics card nvidia GTX 860M / was tested on Intel card too, but without any change).
Here is the link on YT video, which tries to explain this problem a bit, though it is always better to actually "feel" it. I have not tried to show you how much laggy it can get as I do not really want to do that (I wouldn't be even able to turn off the recording probably).
I have tried the things you guys suggested but without any positive results. Also tried to switch on compatibility mode for TB, no results too. TB is simply 'not usable' to longer work, which requires changing focus into buldozer / other apps.