New P55M-UD4 won't boot in AHCI mode - please help!

Hello - I sent this issue to Gigabyte directly, but I figure it can't hurt to ask here as well. I get the feeling that Gigabyte support is a long wait for a train that don't come.

I have encountered an issue with a new build based on a GA-P55M-UD4. Just recently, the machine began to hang when the SATA AHCI bios is loading.

More specifically: when that SATA AHCI loading screen appears during the boot process, the machine hangs exactly when the counter in the upper right hand corner reaches "23." At that point, the boot process fails to discover my drives and the system won't boot.

By hitting the clear CMOS button on the motherboard, I can revert back to the original, default BIOS and the system will boot again, with Windows and everything functioning seemingly normally. However, if I set the primary SATA controller back to AHCI mode, the system the issue will emerge again.

I cannot continue to use IDE mode for the SATA controller since I require TRIM support in my system, which in turn requires AHCI mode. How can I correct this?

More details on my system configuration: I am running a Core i7 860, 8GB DDR3-1333 1.5 CAS9 RAM, Sapphire Vapor-x 5770, Windows 7 x64. I have a total of three hard drives: an OCZ Vertex 60gb w/ FW 1.4 on SATA0 (this is the system drive), and two WD Caviar Black WD7501AALS 750GB drives (storage only) on SATA1 and SATA2. The secondary Gigabyte SATA controller is not in use, but enabled. I have consistently used the AHCI setting even during the OS install.

Through updating the BIOS from F3 to F6, and updating the controller driver from the standard Microsoft driver to the Intel driver Gigabyte provides, the system continued to work fine in AHCI mode. The issue began after I accidentally set one of the WD storage drives as an "active" partition. By using the CMD prompt in the Windows repair CD to load DISKPART, I was able to set the correct active partition again. Upon that reboot, the machine began displaying this issue.

I have tried reflashing the BIOS, and flashing back to F5, to no avail.

Any thoughts? Thanks all!