Ping Fluctuation with Wired Ethernet Connection

Am I the only one experiencing extreme ping fluctuation while playing Rocket League? I play on PC with a wired ethernet connection, just bought a brand new CAT6 wire with 400mbps internet speed and I been having this issue for over 2 weeks now. I have never had any issue before whatsoever. Just wondering if any of you are experiencing the same thing, if there's anything I can do to solve this reallt annoying problem. The Latency variation pops up 1 or 2 times in game and sometimes even though it's laggy it won't pop.

So far I:

> Changed my DNS

> Bought a brand new CAT6 wire

> Changed the Input Buffer to CSTS in game

> Restarted my router multiple times

I have already tested my ping and everything on multiple websites and all say "Excellent". I don't know what else I can do. I play on US-East servers.