2013 F150 speaker help

Hey guys, I just bought a 2013 F150 with the premium Sony sound system. Obviously it does not have crazy good bass or anything but it is decent for a stock system. I am having one issue with the system as a whole though. When I turn the music up loud and the bass starts to hit it automatically adjusts the volume of the door speakers down so that it is not very loud. I can only assume it is doing this because it does not have enough power to push the sub and the speakers at a high level. What can I do to fix this without replacing subs or speakers or is that the only way?