This question has perplexed me from day one. What I have been able to assume from what others have posted...
Theoretically speaking you could run 3 ACs off 50 AMP shore power. If you have 50 AMP service to both sides of a split panel that would total 100 AMPs x 120 volts = 12,000 watts or 6000 watts on each side. To round up if a 15K BTU AC pulls 3000 watts to start and 2000 watts to run, you could start and run two ACs on one side of the panel with the third AC on the other.
Practically speaking the panel and AC are wired to protect the 5500 watt generator which can only handle two ACs at a time, so you cannot run three ACs at the same time. Some have suggested ways to re wire but I'm sure it's set up this way for a good reason.
The Cyclones have a switch to select which two ACs you power at any one time. Some SOBs have load management systems that do this automatically, but still only run two ACs at a time, even on shore power. I remember a post where Jim talked about Heartland offering this same type load management system, but I have yet to see one.
I would be interested to read any additional comments or concerns and look for the day when the manufactures offer a true three AC fifth wheel / toy hauler.