What you're seeing there is called "texture loss". In order to fix that you can try one or more of these steps:
-Go to your lspdfr.ini (which can be found in your lowercase lspdfr folder within the GTA V main directory) and set Main.PreloadAllModels to false.
-Remove any very high poly vehicles you installed into your game (Use openIV to open a cars .yft file for example sheriff2. You can see the amount of polys the cars has in the top left corner. Anything above 200,000 may cause issues)
-Downgrade 4k textures (Open the cars .ytd file through openIV e.g police3.ytd and drag the file that contains the texture to your desktop. Use a picture editing software of your choice to change the resolution from 4096*4096 to 2048*2048. Save it to your desktop and drag them back into the OpenIV texture editor. Hit "save" afterwards.
-Simply lower your graphic settings a bit and see if that already helps