This is a known issue for a lot of people.
Other than repeating that you should check that you have win 7+ and 8 gb of ram, and that you are not running programs in the background while playing GC3, I don't know much else to say except I was rather hoping this would be better in beta 4. It's not a huge problem for me, only freezing every hour or so, but I can playing GC2 for days with no issues. Of course I haven't tried an immense map in GC3 yet either, freezes may be much more frequent.
The problem with these random freezes is that they are nearly impossible to troubleshoot. You can submit a ticket though, just to let them document it.