displayport to hdmi at 75 hz

Hi, looking for some advice. I have 3 of the same, new, Asus VA24EHE monitors, and the monitor is supposed to support freesync at 75 hz. I am not able to get that work work at anything higher than 60 hz. All three are plugged into a brand new MSI AMD Radeon 5500 XT MECH 8GB, with display port to...