Hi @Jedidiah,

Thanks for joining the TP-Link Community. 

Congrats on the fiber upgrade! Unfortunately, although 5 GHz Wi-Fi offers greater speed and bandwidth, being a higher frequency, it is much more susceptible to signal degradation when passing through obstacles such as walls than a lower frequency like 2.4 GHz.

That being said, it sounds like you were able to make it work until the speeds started to decrease. In your case, you may have originally been trying to avoid a double NAT scenario (more than one router in the same network). Apart from the EasyMesh route you took, another option would be to use the Access Point Mode configuration for the Archer AX1800 unit(s) that you don't want to operate as a router.

It is important to note that in Access Point Mode, the Archer AX1800 needs to be wired via Ethernet to your existing LAN. For more information on how to set up the Archer AX1800 in Access Point Mode, please see our FAQ here. 

Since the Archer AX1800s will utilize Ethernet as their backhaul, this will help ensure optimal speeds for connected devices.

One thing to keep in mind while using a unified/single SSID is that the 2.4 GHz and 5 GHz bands will appear as "one network" for your wireless devices. The devices will then roam between 5 GHz (faster, shorter distance) and 2.4 GHz (slower but greater range) at will - depending on the distance from the routers and each device's individual roaming algorithm. Separating the 2.4GHz and 5GHz SSIDs may be worth considering in the future if you encounter any issues with your devices preferring the slower 2.4GHz band too often.