The problem is that you're in Oklahoma. It would only be worse if you were in Texas this year. The reason it's different on the different fan speeds (worse on "hi cool") is that the greater fan speed moves more air across the coils, dumping the heat from the air in the trailer into the coils faster than your compressor can push refrigerant through. On the Lo Cool fan speed, you're just not moving as much air across the coil per unit time and the temperature differential from where the refrigerant enters the evaporator to where it exits won't be as great.
If you're able to keep the interior at a livable temp you don't have any other problems, just make sure the coils are clean inside and out and try to hang out on the side where the colder air comes out the vents... hopefully the weather's finally about to get back down to double digits!
Il Carriaggio — 1975 Argosy 24 | Il Progetto — 1976 Argosy 28 Center Bath | WBCCI# 15566
He has all of the virtues I dislike and none of the vices I admire. — Sir Winston Churchill