Diagonal Tearing in 1920x1080 but not in 4k!?

[rasmoothstep]

I am trying to play my modded skyrim in 1920x1080 to get 40-60 fps but I sometimes get diagonal tearing (like upstairs in Dragonsreach) but what is strange I do not get it running at 4k (but obviously only maybe 20 fps).

 

I am using OneTweak to run in borderless windowed mode but on or off it doesn't change the tearing.

 

Any ideas?

[rasmoothstep]

I solved the issue by not running in windowed mode at all and not using OneTweak.  I am also getting better FPS. :)