Are you in overdrive or distortion mode? I get unity at about 1-2:00 with the Drive at noon on my yellow (low gain) channel in overdrive mode. Distortion mode (dipswitch two on) will drop the volume a bit further, and I would recommend the high gain mod if you intend to use it.
If you really have to dime it to get unity gain in overdrive mode, there's probably something wrong with your build. If it's the same on both channels, my first guess would be a wrong value on a component. Tell us more about your build -- any subs or mods?