I have this same TV, bought in Walmart on t-givin' for $300. I can confirm this TV runs at 4k / 60 Hz. This TV is pretty darn good, even for twice the money, but there are some things you need to know and change in settings. I assume you are using a modern graphics card? I use a RX-470 and it works fine, but not right out of the box. The reason I ask if it's modern is that I want to know if you have HDMI 2 and HDCP 2 or higher. If you do, or if not sure just want to try anyway, you need to switch the HDMI mode from Legacy (default) to Normal. The difference is HDCP earlier than 2.2 for legacy, or 2.2 for "normal mode" (not backward compatible). Give it a try and let me know if it works. If it don't, I have some other ideas I can share but don't want to create a text wall.
Here's how to het to HDMI Mode.. it's not easy to find.....
Options -> switch to middle tab (top) then down to Setup -> TV Settings -> Installation -> Preferences -> HDMI Mode
Here's how to switch between PC (best for PC gaming) and HDTV (obviously for TV)......
Options -> switch to middle tab (top) then down to Setup > TV Settings -> Picture -> Mode Selection (PC / HDTV)