ATI Firepro v5700 only outputting 800x600

So I got 2 computer for free that a company were throwing out that I've decided to make one into my first hackintosh for practice for when I have the money to make a hackintosh I want to actually use.

Using this guide (https://www.reddit.com/r/hackintosh/comments/43hzgd/ancient_g31mes2l_board_working_with_el_capitan/?utm_medium=android_app&utm_source=share) I appear to have everything working. However the graphics card seems to only be outputting 800x600 over displayport and it has graphical issues when it first loads and on full screen youtube.

Obviously, the guide isn't for this graphics card and I can't find anything useful about it online, does anyone have any ideas of what I could try?

submitted by /u/confused730
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