Why can’t I use this monitor full resolution at 60hz on my 2013 Mac Pro with OS X Mojave?

https://www.samsung.com/us/computing/monitors/uhd-and-wqhd/32-uj590-uhd-monitor-lu32j590uqnxza/#specs

Says 60hz on the site, tried HDMI1, HDMI2, FreeSync, tried various HDMI cables, even bought an HDMI to Thunderbolt cable to try instead of HDMI out of the mac.

What gives?

My old mac mini can drive my 60″ TV properly, but my Mac pro can’t drive an UHD display? Seems like I should be able to do this….

This is the only resolution I can get 60hz at:

displays

EDIT Answer marked below. For anyone wondering:

thunderbolt