AMD 280x (same as the HD 7970) uses ULPS. It lowers the GPU speeds when it doesn't need all of it's speed to reduce power consumption and heat.
You can leave it as, it should run itself at full speeds when you're gaming. If it isn't, you can manually turn ULPS off but the best way to do that requires a registry edit.
If you want to disable it follow these instructions:
https://community.amd.com/thread/176003