Mac Pro 3.1 applications stall and crash after new graphics card installation

I have a 2008 Mac Pro 3.1 running Yosemite 10.10.2. The only performance issues I've had have been graphics related so after a bit of research I installed an Nvidia GTX 680 mac edition which should be more than adequate. However, I now have frustrating issues with applications such as Safari and FireFox freezing regularly and crashing occassionally. MainStage will not even open. VLC takes several minutes to open, but then operates normally. I have tried many online searches to find a solution but I appear to be the only one suffering from this issue. I'm not even sure it is the graphic card installation that is the problem (although it is likely) as there was a security update for OS X at about the same time all this started (the weekend). I'm really not sure where to start trouble shooting this problem. If anyone has some pointers I'd be grateful.