Alternator/generator/regulator problems of the 2011 Chevrolet Silverado 1500

I have had an ongoing problem with the electrical system in my truck. First time it happened I was leaving my house and as soon as I got a few houses down the road my door locks started unlocking and locking themselves over and over and the speedometer gauge was all over the place along with the rpm gauge and the road up would turn off and on and the brakes would lock up and then release and it did this until I was able to pull over and turn the truck off. Once the truck was off it wouldn't start again. I had taken the battery out to be tested and it was fine. The alternator was fine and as far as I could see the negative and positive cables from the battery were clean too. I've traced the ground and it doesn't appear to be in bad shape either. Well after I was able to get it back to my house it sat for a few days and after a couple days it randomly started back up. Took it to the local chevy dealership and they said there is no problem everything is good and they couldn't recreate the problem. They said it could be the aftermarket head unit. Well once I got my truck back the head unit no longer works or gets power? well now a month later same problem and the truck is totally dead but battery and etc is fine.