I've run UO flawlessly on lots of AMD cpu's.
The graphics card that you have probably requires a supplementary power connector attached to it from your power supply. It might not work quite right if this is not attached. Something to check.
Other than that, I would check the power supply itself. There are usually readings in the BIOS that show the voltage levels. The +12 should be around 12.05v not 11v, for example.
While it's open, go ahead and turn it on and make sure all fans are operating well, not stopping and starting. (CPU fan, video card fan, power supply fan, motherboard chipset fan, case fan(s).) They turn pretty much invisible when things are working well. A flashlight sometimes helps.
Another thing to try are different 'official' drivers for your motherboard's chipset.
I would definitely run Memtest86 on this system as it seems to be a prime candidate for defective RAM chips. (The most common cause of general system instability.)
Also, try setting your CPU to non-overclocked settings.
Lastly, you are not testing the smoothness of UO in Luna or somewhere like that are you? If so, all machines lag/jerk/chop in spots there, can't be helped.