Can someone please help me understand why a brand new Mac pro with an Nvidia quadro 4000 graphics card cannot support what my 2008 Mac pro with an Nvidia geforce 8800 can?

1 triple head to go running a 3 projector blend at 1280X800 each projector, and then a single screen running at 1280X800. I had mine running this configuration for 5 weeks, with no problem. Now this one is in here and I can't make it work to save my life.