[Stumpy75]

There's a lot more knowledgeable people here than I am on electricity. I don't know your level of electrical knowledge or skill, and mine is limited to some basics. There are some good electricians here.

The cord you are using "should" be ok, but confirm that it is 10 gauge. It should be stamped on the outside of the cord.

That being said, I would start looking at places where there might be a bad, corroded or loose connection. Do any of the plugs feel warm after running the AC for a while? Check all the cords spades for corrosion and/or discoloration.

I would start at the 30A wall plug and measure the voltage right at the plug with the AC running. This means sticking the probes of the meter in past the plug to contact the spades of the cable(and are you willing and able to do that?). If everything is ok there, then go to the next plug(between the two cables) and try it again, looking for the voltage drop.

Next spot would probably be where the cable connects to your trailer, and will probably require you to pull or open up the power panel in the trailer. Lots of reports on this forum of loose connections behind this panel.

All of the above is assuming that the AC is running ok, and not drawing too much power. An amp meter would tell that fairly quickly...

That's my 2 cents.

Hopefully, one of the sparkys here will jump in with a lot more info.