what exactly is it doing. Is it throwing codes? Is it shutting down? Is it telling you there is a communication problem? Does it say it has low voltage? It wont start if it is less than 10.5 volts. Maybe a CanBus problem.
Everything will quit working engine stays running. The only thing that works in the cab is the corner post. The gs3 shuts off no power to power strip lights don't work. The only thing that comes on command center is low voltage and flashes stop. You can not navigate to read codes. It did it three times today,don't really know what did to get it to work again.
Also look at your fuse block. The positive cable that comes from the battery to the block. If there is 2 nuts holding on the cable, check to see if they are tight. If it isn't tight remove the outer nut, throw it over your shoulder, then reinstall the cable behind the first nut. There should only be one nut holding it on.
Also check hardware holding on alternator b/c this is suppose to be the ground.
Is the debris screens plugged up. If so clean them out and see if it helps.
I have diagnosed this exact problem before and it ended up taking a new alternator.