Thin face UV Flickering problem

Instead of using cubic uv mapping in blender, I uv mapped my, let's say, cube, from one perspective.
As expected, only 2 faces, front and back, got properly uv-mapped and the rest 4 faces have, again, as expected, stretched pixels from corners of those first 2 as texture.
There should be no problem if I wanted to achieve this stretching, and I want.

The problem is that those 4 faces appear to flicker in Unity engine. The effect is very similar to Z-fighting, but I suspect something else is responsible for this. Maybe shader? I use standard shader. Maybe texture settings? I've tryed everything... ok, not everything, but it can't be texture import settings.

Anyone with similar expirience?
Thak you for your help, of course, only if you can help me!

 

EDIT: Please, delete this post.

The problem may be duplicated face due to using extrude tool in blender inproperly. I just tested this problem with a cube and everything seemed fine, so my only thought on this is that I must improve my modelling skills in blender!