I'm surprised at what the tech said, because you are correct that 50 amps in a RV gives you 50 amps on each of two legs. See here
for a quick article covering this by a RV electrician expert.
Since your ACs do work properly at times, I wonder if the cycling is perhaps being caused by coil freezing. See here
for an article describing how to diagnose that problem. Although I've never heard that coil freezing would end up with your unit blowing warm air (unless perhaps you have your thermostats to run the fans all of the time rather than on/off in auto mode).
Good luck with figuring this out!