Default Monitor 2 Output on Mac Pro?

I have a 2008 Mac Pro with the stock ATI graphics card. Recently I have been getting some lagging and freezing (2 sec of freezing) while working in Pro Tools. It's definitely the graphics card, because if I switch to the other monitor output it's smooth sailing. Now, if I hot swap them (probably not a great idea) it will sometimes work, however, when I start up the monitor is not recognized. Also, if I "detect displays" it doesn't always recognize the display. I'm only one single monitor on 10.6.8. It gets really frustrating having this thing lock up every 10 seconds. I just want to use Output 2 by default. Anyway to do this? Or must I drop the money for another card?

Thanks

If you think the card on the wayout best replace with a like for like. Macupgrade do have the replacement type last time i looked. otherwise as you mention the spare slot still works then you could use a kvm splitter gadget that allows two monitors to work on by switching.