I think the AC units struggle to cool down RV if the inside is hotter than outside to start. Once inside has been cooled AC does a better at keeping up. These AC units will only provide a 20 degree drop at best. If it's really hot and humid it might only drop 10 degrees.
We added these pillow like things from Camco to insulate the roof vents. We also use an oscillating fan these things seem to help. If we are running both AC's because it is so hot. We open vents that blow straight from the AC instead of using ducted vents. I found that we had cold air blowing outside from the front cap down by the tongue when using ducted vents. Dealer was no help in this matter.
2016 Ford F250 XLT 4X4 6.2L
2015 Rockwood Signature Ultralite 8329SS
Nights camping in 2016: 19 nights
Miles traveled in 2016: 2,575