I need help with my a/c power/generator.

I have a new 2014 riverside retro travel trailer with a side wall mounded a/c unit. It runs fine when plugged into regular outlet, but when running on generator it will do fine but after a while just stop. At which point there is power to everything except the a/c unit (no light up numbers and buttons do nothing). The GFI and circuit breakers are not tripped). It remains off until I hook up at regular outlet (usually >10 min drive away).

I figured it was due to not having enough power in the generator, so I bought another- now running on two Yamaha EF2000iS. 4000 watts should be plenty of power. it is still happening. I took it to dealer who checked electrical system- they couldn’t find anything. Could it be the Parallel Power Cable, although they come from Yamaha. I am at a loss of what to do or where to turn.

Please help.