I think my truck might be losing power. Occaisionally while at a stop, my check gage light will come on, but there's no gage that's at a "check" level except my charging gage is right around the bottom corner of the battery icon. It's low, but not in the red. I took it to Advance and they checked the battery and alternator and they both seemed fine. The truck's cranking fine and always has, but my stereo has to be turned up more and more to be able to hear it and my power locks work erratically. The locks have been an issue for a little while and the stereo isn't the best quality, but I'm thinking they may be signs of something else. I also have a small amp and 10" sub wired to the power dist box and a couple of small lights that I rarely turn on. What can I check to see if I'm getting low volts without throwing parts at the charging system?