I recommend you to review and follow the instructions on this article:
Especially, make sure to be using the latest driver for the monitor that you connected, update the BIOS of your computer, test using the special driver posted there and use a direct connection between the computer and the TV.
I know it's a bit late as the question was a couple of months ago but thought I'd reply in case it's still not sorted or anyone finds the question while looking for a similar issue (like I did!). I had the same issue on my LG TV with a motherboard from the same Gigabyte series, had to set the scaling to 65% to see the whole screen. Turned out that the TV is set to 'overscan' by default, in my case choosing the 'just scan' option on the TV fixed it, I think Sony TVs simply refer to it as 'overscan' so try and find that option in your TV menus and turn it off, others may call it 1:1 pixel mapping. Hope this helps.