94 Blazer electrical questions

I have a 94 chev blazer with a 350. I keep having problems with my truck loosing power, if you watch the battery gauge anytime I have multiple things running like the blinker, lights or windshield wipers the gauge drops. I have replaced the battery and alternator. Any body have any other ideas? Also for some reason my now my brights only work on my lights and my reverse lights don't work anymore. Thanks For the the help