Graphics problem that I cant find anywhere else

Hello there, I have problems with graphics that happens every 3-4 minutes and it lasts for 2-5 seconds, then everything is ok and again problem, again and again. Suddenly i have pixels all over my screen, and the game looks like its 240p or smth, I have ultra/high settings and easily getting 100 fps,
Everything is okay and then for 2-5 secs like i said THIS happens: Imgur: The magic of the Internet
Anyone knows what to do? I would like also to change settings, but every restart i make Forza doesnt remember my settings and thats another problem… pls help ;-;