If an amp overheats, it is 99% of the time related to either the install or electrical. If you don't have big enough wire, bad grounds, gains turned up too high, not enough voltage, not enough air circulation, etc.

As someone already mentioned, it could be quite a few things causing it. I would start with the more obvious and easier to diagnose and go from there. More than likely it is an install problem. Turn down the gains, be sure you have good grounds, and be sure you have proper size cables powering the amp. After that, things get a little more complicated to diagnose.