Charging System Indicator Light

I started up my 97 Jimmy to come home from work tonight and my charging system indicator light came on. It stayed on for the full 30 minute commute and by the time I reached my driveway my headlights and gauge lights were dim to the point of being useless. The first thing to check here is obviously the alternator, but are there any other possible causes? I'd like to know what to check so I can avoid paying Pep Boys $40 just to find out what the problem is. The truck is also idling strangely. Every 10 to 15 seconds the engine jumps from about 750 rpm to 900 rpm or 1000 rpm for a second or two. I doubt this is related to the power issue but I noticed it at the same time. Any help would be greatly appreciated.

Most likely the alternator is faulty. Some auto parts stores will check them for free, Advance auto parts, auto zone etc, call around. You'll need to remove the alternator and bring it to them to test it. The erratic idle is probably caused by low voltage. Get the charging system working first.