Apple has released Mac Pro EFI Firmware Update 1.3 which fixes several issues to improve the stability of Mac Pro (Early 2008) computers.
After the firmware is successfully applied to your computer, your BootROM Version will be:
MP31.006C.B05
You can confirm the version of the Boot ROM installed on your computer using System Profiler.
To complete the firmware update process, please follow the instructions in the updater application (/Applications/Utilities/Mac Pro EFI Firmware Update.app). The updater will launch automatically when the Installer closes.
Mac Pro EFI Firmware Update 1.3 is available via Software Update and also as a standalone installer.
More info and download link (1.76MB) here.