Does anyone know how to fix the rainbow and not “sharp” text. Using dual monitors on an RX 580.

Hello. Recently installed High Sierra to dual-boot with Mojave, but I get this rain owing text, and overall the display does not seem nearly as sharp as in Mojave. Any help would be appreciated.

Specs: Intel Core i5 8400 AORUS Gaming 3 Mobo Gigabyte RX 580

Picture: https://i.imgur.com/rpilgOP.jpg

Will upload EFI folder when I get home.