So I had my 480 for about a week with flawless performance and then I put a Zalman ZF3000F on it and I started getting down clocking all the time to something like 405/375 (core/memory). I started thinking what changed between that cooler swap and before and I finally figured it out. HD Audio, that was the only thing different between before the cooler and after; because I updated the drivers after putting on the cooler and the ones before did not have HD Audio. Now I know some of you use the HD Audio option so this isn't a complete fix. But for all the people who do not you should try uninstalling HD Audio in control panel and do the required restart.

I thought I had screwed up somehow during the aftermarket install even with two people installing it and years of experience from both parties, but I knew something else had to be causing this. I've read countless threads of people with the same problem and I hope this helps you if you do not need HD Audio out of your mini HDMI slot.

Good luck