FIRST - DUDE - You gotta
learn to make a paragraph, OMG!!! Is your post hard to read
I read through it Six times, I think I'm understanding some of what you're saying. So, how old are the batteries? If you put a good charger on it and it acts like they're charged I don't know why your gauge would go "lower the whole time" as you drive...
Maybe you could get them load tested, one at a time to be sure.
The GPs do draw almost 200A so, I wouldn't be surprised that you can see the change in brightness when click off but, if everything was it should be (batteries/connections) it should be able to handle it all.
How about all those connections, including the wires on the back of the alternator? Make sure they're all Clean, Tight, and Greased.
Could you have water in your Gem module? Has it been raining a lot? (windshields are prone to leaking in the bottom corners and dripping into the Gem)