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I got a new MG28UQ 28" 4K monitor and I plugged it into my mid 2015 15" retina MBP using a mini display port to HDMI cable. The monitor itself reports it's receiving image at 60Hz, however, Settings > Displays only lists 30Hz under "Refresh Rate". If I lower down the scaled resolution to 1600 x 900, then it starts using 60Hz and the mouse problem goes away.

I'm using an Insignia Mini DisplayPort to HDMI cable that states it can handle 4K.

What am I missing?

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  • The first thing I would do is not use HDMI because there has to be a signal conversion. Go native mDP to DP
    – Allan
    Nov 24, 2017 at 11:16

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Any scaling that is not exactly half of full resolution will introduce strain on the GPU and cause sluggishness. So on a 4K monitor your choices are either 1080p or 4K. I find neither acceptable. If you want 1440p (looks the best imho) you have to purchase a less crisp 1440p monitor or drop the big dollars for a 5K monitor and then run it at crisp retina 1440p which is exactly half of 5K and will not strain the GPU.

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I had to same issue and switched to mini display to display kable to connect my MBP to my 4K Dislpay now it supports 60 Hz.THe only problem is when i use a scaled resolution my screen is laggy. =(

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I was having a similar problem using a Dell U2720Q monitor, and the solution outlined here worked for me:

https://www.dell.com/community/Monitors/U2720Q-MacBook-Pro-29Hz/m-p/7533720#M124865

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