Hikerdog has the owners manual so it answers the question about the slides needing extra HP, voltage that is by suggesting the engine be running.
I would have a voltmeter on those battery banks with engine running, engine off, shoreline connected, and shoreline and engine at the same time. This will take a bunch of voltage measurements but should tell us all we need to sort it out.
Hence, my suggestion of having a notepad and camera.
If the slides are slow with the engine and shoreline connected you will need to take some measurments on the wires that feed the slide.