On my HD 4870, I use manual fan control in Catalyst. If your fan still runs weird with that on, it may be faulty. Keep in mind, there may be other solutions, I'm not familiar with the newer series cards.
What do you mean by slow? Are you having a heat problem? Modern cards control the fan automatically so for instance my 6950 only runs about 30% at the desktop or just browsing but will speed up when playing games and such.
Well for starters it doesn't spin up on startup and then when I use afterburner to manually control speed it barely speeds up so I have to play with it to get it to properly spin up to the set speed. If I leave it in auto same problem and it won't spin fast enough to keep the gpu cool enough to play my games.