MP 1,1-5,1 Mac pro (early 2008, 3,1) gpu upgrade

[HeadstrongZodiac]

I recently bought a second-hand mac pro 3,1. I installed dosdude1's mojave patcher onto it, and the screen started tearing (it wasn't when macos high sierra was installed). I assume this has to do with the gpu, so what would you all recommend I buy for it? If it doesn't relate to the gpu, the. what could be causing it? (The gpu is the default hd 2600 xt)

 

[OS6-OSX]

Using a flashed K5000

 

[HeadstrongZodiac]

Looks good, but are there any cards that don't require flashing? My knowledge is pretty weak on the topic.