If that amp is 3K watts RMS, then if you set it at clipping, you might be sending well over 3K watts to that sub. That sub probably won't last long.
If you don't need the full RMS output of your amp, here is how you use your gain to drop the power output. This way you can also back off a number or two on the head unit, and you will have the option to put a little more into it for the right song. Plus your head unit might be distorting the signal at full volume. If you don't have the equipment to test your head unit's signal quality at higher/full volume, back off a number or two when you set it, and you can make sure your head unit is not causing distortion.