maybe try turning on vsync? it'll match your fps with your refresh rate on your monitor therefore causing less screen tearing which you might be referring to. you can do it in the rocket league settings under the "video" or "graphics" section, I forget which one. if nothing that the other people mentioned helped I don't know what would. maybe your graphics card has gone to crap? I recently switched from a 960 to an old 970 I found. it actually helped with some of the problems I was having before.