Putting a lower t stat will NOT lower your engine temp, if the motor is running at 230 doesn't matter if your running a 160 t stat, t stats are for getting your engine at operating temperature faster.
you have a cooling issue, most engines run at 210, your have to address the cooling issue not cover it up.
I see temps at 220-230 going up 6% grades, flatland should run at 210.
Im in NM, so average temp here is 90-100s all summer long
Radiator could be clogged, or just dirty with bugs and dirt on the outside of it.
Fan clutch might not be engaging
2005 Tiffin Allegro Bay 37DB
W22 Workhorse Chassis 8.1