So what works best for me so far to avoid total lock-ups that require a hard reboot (this happens more) or CTD is to save often and every 15 min or so quit to main menu and restart game. I know this seems like a pain, but since I get whole system freezes more often, that require more time to restart, this is a much better option. If all I had were CTD's then I wouldn't bother. By doing this I can get hours of game play without freezes. Hope this helps someone else.