New Spectrum customer with a 1 gig plan wondering why my internet over WiFi is bad and the speed spikes constantly?

Sorry if this has been asked before but I moved recently and spectrum was the best internet option in my area, so I signed up for the 1 gig speed plan and I’m having some some frustrating issues with the WiFi constantly slowing down to the point of barely loading anything, whether that’s on my phone, laptop, Roku, or online games.

I’ve run multiple speed tests and typically get 300+ mbps over WiFi which is fantastic, but the problem seems to be that it can never maintain that speed consistently.

I’m wondering if the issue is from the cable lines themselves having a faulty connection, or if it could possibly be the WiFi router that’s causing this? The router is in my downstairs living room and the connection is really weak upstairs, which is not something I’ve dealt with in the past with Google fiber or Xfinity. I usually get 2 bars of WiFi and frequently my phone disconnects from WiFi altogether and switches itself back to 5G.

For some additional context, I play Rocket League online, which displays your ping. When the WiFi is working normally, I only have around 30 ping max, and the game runs smoothly and fast. But I can’t even get through a single 5 minute game without the ping spiking red into the 500+ range.

I’m planning to call spectrum to hopefully have someone troubleshoot with the issue, but honestly based on my experience with their technicians setting things up for me and having to make 3 separate appointments just to get it working, I would much rather save myself the trouble if all I need to do is go out and buy my own WiFi router to fix the issue.

Pretty disappointed in the service so far but hoping this can improve