I am pretty sure it will not impact running both AC's as it was built that way, but I would find out who makes the Energy Management System and fins out how it works.
I think the impact will ultimately be that you can run everything like normal at the same time. I tried to get a RV mfg to install a 2nd AC 11000 BTUs into an existing new RV with one 15000 BTU Onan 4000 and they would NOT touch it.
I eventually bought a unit with 5500 and two 13,500s. I need every bit of it too. Also from what I read the Onan 5500 are a lot quieter than Onan 4000
But you seem to have no choice. If it were me, 2 ACs is 2 ACs and if both work you good as gold. I am sure Thor knew what they were doing so I would not sweat it too much. With that said, I would HAVE to be in one on an extremely hot day and run both both ACs to see how it took to cool down with Slide out. I have been in brand new units that never cooled down and it was only 95* outside
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