So.... I have the same mobo. I bought it with a Phenom II X3. I used to have an Acer 24" that did 1900x1200 but it died just shortly before this was built and it was replaced with a hannspree 25" that does max resolution at 1920x1080.
I am a microsoft partner and got my Windows 7 Ultimate license about a month ago. Heres my story as it differs slightly from your own.
So.. originally loaded Win 7 as only OS on this new machine :
Gigabyte GA-MA785GPMT-UD2H
AMD Phenom II X3 720 2.8GHz 3 x 512KB L2 Cache 6MB L3 Cache Socket AM3
4 gb DDR3 1333
Zalman HS
Thermaltake Element S case
OS is a 300gb Sata2
3 x 1TB HDDs for data
What I ended up with after getting all drivers installed was that CCC would show that my monitor was displaying at its max resolution 1920x1080 but it was surrounded by black bars. When I would log off or reboot, right before I logged on it would show the login screen using the entire monitor but once logged in it would resort to its "letterboxed" image still showing that I was running the full resolution.
I decided to go back to Vista Ultimate and did a dual boot on same OSdrive . I have been running Vista Ultimate OK since then with one exception. The problem did follow this Windows Install, however, I found that through the CCC I was now able to see multiple refresh rates and select them vs in Win 7 where I can't change anything (rather, making a change does nothing, in fact after hitting ok or reply it goes back to default settings not allowing your change to take effect). But for the monitor to show correctly, after loggin in I have to go into the CCC and change the refresh rate from 59 to 60 hz and vice versa every single time I reboot. It doesn't care which refresh rate it has at boot, it will go back to letterbox until I make that one change and then bam, full screen again.
I sent in requests to Gigabyte complaining about compatibility and they told me basically to shut up and wait till the full win7 release date. I tried again recently and still no change.
I've got a perfectly good copy of Win 7 Ultimate jsut waiting for me to use but I can't .. I can't force myself to use it like that. its just too upsetting.
WHAT A PISSER OF A MOBO