I just received a RMA'd rev 1.0 GA-990FXA-UD5 from Gigabyte. The symptoms I was getting were:
PC 100% stable AMD 1100T over clocked to 3.8Ghz. 4xPC1600 DDR3 16GB.
Upgraded CPU to AMD 8350. Memory errors, freezes, failed memtest, frozen memtest, unable to run at PC1333 speeds reliably. Tried new memory (2x8GB from Crucial and Corsair) same issue. Finally got it stable by disabling turbo core and manually setting voltage higher to compensate for vdroop and memory at 1600. I was convinced it is a vdroop issue on the rev 1.0 so I got hold of a rev 1.1 version of the board with LLC control in BIOS and it ran all previously failing memory at 1866 speeds and the 8350 over clocked to 4.6Ghz (Turbo disabled).
Now I haven't tested this returned board (Staying with my 1.1) which is my original rev 1.0 (Checked S/N). But I can see it has had a resistor changed near the voltage controller next to the CPU socket. I know there was a DIY fix (If your good at soldering and have very good eyesight) that replaced a resistor on the UD7 which disabled vdroop on it's rev 1.0 so I suspect they have simply replaced the same resistor on the controller to do the same here.
I recommend RMA'ing it if it's under manufacturers warranty to get this rework. If not the rev 1.1 sorted it here.