On second thought, you should be able to use Phenom ii according to Gigabyte's website. http://www.gigabyte.com/products/product-page.aspx?pid=... I think you will need to update to rev 2.0 first. It does say AM3 ready on the front, do you remember if the box your motherboard came with mentioned any of this?
The Phenom II X4 955 has been out for a longtime and so I doubt that Gigabyte will suddenly add support of the CPUID; my observations are none of the Phenom II or Athlon II CPUs are listed. Further, with a single exception no 4000 System Bus(MT/s) CPUs are supported. Most importantly, there are physical differences between the rev 1 & 2 -- look at the images and count the MOSFET / VRM one additional phase makes all the difference.
Ya I did look at those lists, tis how I knew that rev 2.0 did support em. Was just wishful thinking on my part that I might be able to get a good performance boost with just a CPU upgrade.
Mine is still "ok" for most games. I just know the next crop with BF3 and PS2 and the like are gonna kick it square in the teeth. If I could have gotten away with sub $150 upgrade for a good boost I would have done it. Past that I am sure I am better off with whole new MB, CPU, RAM, & Video card. I'll just have to bite the bullet and build a new rig for sub $1k.
Now I'll just wait on new AMD to see if it or Intel chips are now the "Bang for the Buck".