Always make sure your MoBo chipset drivers are up to date as well.
They are often forgotten.

You have not said which UT renderer you are trying to use, or if you have updated from the ancient basic renderers.
This may help.
UT99.org | TUTORIAL: Tweak Your UT Graphics & Audio To The Maximum : Tips, Tricks & Tutorials

If you want some software to tweak the GFX drivers, then there are a few choices.
My Unreal - Tweak Windows and ALL Graphics drivers