R7000 slow speeds

I have been noticing slow Internet and WiFi speeds through my R7000 router. I assumed it was through my ISP's end, but I called them and they had me troubleshoot through things and we determined that the issue was being caused by the router, not their modem or service.

We have Spectrum Ultra which gives us "up to" 400Mbps, but when we first got the service we frequently saw around 500Mbps even during high traffic times. Lately (maybe the last month or so), our speed has been around 120Mbps, the max I've seen it at one time was 140Mbps. I am hardwired to the router with 2 PC's and an Xbox One console, plus wirelessly with 2 phones and several IoT devices, all of which have the same speed from what I've been able to test. Hardwiring my PCs straight to the modem gave me speeds of ~470Mbps, typical of what I used to get.

I've already factory reset the router. After doing so, I was still getting only 120Mbps downloads. Although the firmware auto update showed that I had the most current update (1.0.9.88 I believe it was) I noticed there was a more recent update on the Netgear Support site (1.0.11.102) which I then downloaded. After installing the new firmware version, my speeds are still not any better. Most other troubleshooting guides I've seen recommend factory resets or firmware updates, so I'm not sure what else I can do from here.