Alright, so I'm never really worked on a lot of electrical problems, but this one is beginning to tick me off to a point I can't take anymore. When I roll my windows down or up, apply the brakes and even turn on my blinkers my headlights flicker and become dim. They also flicker when I crank my stereo up loud and my subs kick hard. The worst of it is when I roll my windows up or down and they become dim. I also recently noticed the other day that my heated seats no longer work. When I press the button the light for on comes up for a brief half a second then goes away. Anyone have any ideas as to why this is happening, and how I can fix it?

I drive a 2003 GMC SIERRA 1500 ext cab, with a 5.3l Vortec and a Duralast yellow top battery.