Amp is located in the trunk of my car so sun surely isn't hitting the amp. It's sitting flat (not upside down causing the heatsinks to not properly function). Nothing around it/on top of it/etc that would cause problems either. As far as air flow, I dont have any AC vents in my trunk so there really isn't much air circulating around in there.

When playing music... I'm listening to it at a fairly loud volume level usually. I define fairly loud as if the windows are down then you can hear it within 10 ft or so of the car at a soft level (not too soft / you can still distinguish what music is playing).

Gain settings... maybe that is the main source of my problem? Not sure. The head unit puts out 4v preouts... The amp gain controls adjust from 200mv to 5v. Ive got it turned up approximately 2/3 the way (and when I say turned up, I mean if I were to have it at 3/4 the way or fully turned up, the music would play louder)