I would need to know the details/specifications of your computer, you may be experiencing some conflicts with regard to some components holding other components back. Which is called bottlenecks!
Install the latest drivers off the AMD Website,
www.amd.com
The latest drivers will make your graphics card work more
efficiently.
In my
opinion this card shouldn't have any problems running at 1920X1080 at Medium to High Settings with X4 AA or more.
It's a good Card, ensure that the Temperatures are kept in check. Remember the cooler you get it the more
efficiently it's going to run.
Install some 120mm fans on your case if you can, Cooler Master have designed some super cool fans. I
myself use the new Sickle Flow 120mm blue, 2000RPM 90 Cubic Feet per Minute.
All the best!
damnor01