PG278Q Hz Problem, need help please

[falkentyne]

I think your problem is the thunderbolt port, but that seems to be fully mini-DP. I had to google just to find out what it is. Did you contact Asus about your issue?
When you try to activate the external display (PG278), are you clicking the option to disable the laptop display or is the laptop display still in use? I don't know how this works; I have an old Geforce 570m laptop (MSI) and it just has HDMI and VGA.

Sorry if that doesn't help. The problem isn't the monitor, though.