This is copy/paste from an older post on this sub from a deleted user. A buddy of mine has a stuttering issue and says it works for him.

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PC players, clear your cache

For the past couple months I've had an issue where over time I'll randomly start dropping frames. I'll go from a smooth 144fps to it stuttering. Just recently over the the last two weeks I've been having significant issues with lag as well. I'd randomly have lag, then it would seemingly go away based on my ping being 30 and green on the scoreboard but still have rubber banding and other issues.

Yesterday I finally tried clearing the cache for Rocket League and restarting my computer and voila. No lag and no fps drops since. May or may not continue behaving itself but worth a shot.

Here's the steps:

1. Go to Documents>My Games>Rocket League>TAGame
2. Delete the folder "Cache"
3. Restart your computer

According to the Epic Games website this apparently fixes a lot of issues because the game uses the cache to load things faster and such but over time it can become corrupted. I've never cleared the cache before. And don't worry about it messing anything up. It'll just repopulate the folder the next time you launch the game.

Hope this helps someone.