Changing the fluid won't help. If you were having problems disengageing the clutch I'd say maybe give it a shot, since that's the only time the fluid really plays any role in the system, the rest of the time it's at rest and just taking up space.
If you're sure you know what a slipping clutch feels like then you'll have to put in a different one, hopefully something from a reputable company this time. I think you'd have other obvious problems if there were anything wrong with the installation. O'reillys should refund your money.