VGA Card Problems Mac - Pro and Samsung P2350

Hi All i need Help

I use a MacPro 1.1 with 2 Monitors 1 Cinemay Diplay 20 and a second TFT wich is a Samsung p2350. Works fine with OS 10.5. For some reasons i install 10.68 but the Samsung Monitor just work with 1080p. With 10.5 the Monitor run 1920x1080. ? I need the second monitor to work with Photoshop.

I change the VGA Card from ATI 1900 to Orignal Apple Upgrade Nvidia 8800 GT same Problem! :-(

Thank you in Advance for any Help!

Julius