15-Inch Late 2013 is a laggy mess with LG B7

[GigabitEthernet]

When I connect my 15-Inch Late 2013 to my LG B7, it's a laggy mess. Video drops frames all over the place, the UI is incredibly laggy and it's just incredibly poor to use it.

Can somebody explain why? I thought it might be a 4K issue but I'm using the HDMI port and an HDMI 1.4 cable which only supports 1080p and I have the same issue. No issues with other displays. No issues with other inputs on the TV, they look great.

 

[jerryk]

Where the other displays where it worked well 4K?

 

[GigabitEthernet]

Where the other displays where it worked well 4K?

Another TV was 1080p and my Dell monitor is 1440p.

But bemused why it would be an issue when I am using 1080p on the LG anyway?