1989 Other Ford Models engine overheating

I have a 1989 Allegro motorhome with a Ford 460. I have replaced the thermostat with a 160 degree stat, made sure that good air moves through the radiator and the temp gage still raises to 230 degrees. When I drain some collant out to check the temperature it checks 195 degrees. These tests were done while sitting in the yard with a high idle. Usually going down the road it will take about 30 minutes to achieve 230 degrees on the temp gage. How can I get the temp to come down?