Blocky graphical issues and missing roads

Essentially, I'm getting these uniform sized squares at random spots in the graphics. (See images below.) They happen at near and far distances, and more consistently at night. Also, the road just likes to disappear. This happens in Online and Story mode. I've played around with AA and DX settings, but haven't been able to change much.

My system specs:

• Windows 8.1
• AMD Athlon II X4 630
• AMD Radeon HD 7800 (2 GB)
• 20 GB RAM

Solution 1:

So, I fixed it. I don't know what steps actually helped, but I'll post it anyway.

• Running GTA5.exe in "High Priority" from the Task Manager Most important
• Switching DX Version to 11, then to 10.1, then back to 11.

Game Settings:

• Screen Type: Windowed Borderless
• FXAA: On
• MSAA: Off
• Vsync: Off
• Pause on Focus Loss: On
• Pop Density: 10%
• Population Variety: 100%
• Distance Scaling: 10%
• Texture: V. High
• Shader: High
• Shadow: High
• Reflection: High
• Reflection MSAA: Off
• Water: High
• Particles: High
• Grass: High
• Shadows: Soft
• Post FX: High
• Motion Blur: 0%
• Anisotropic: X2
• Occlusion: High
• Tessellation: High