@jazzman831,

Your T-Mobile Router - Is this a Gateway that is also operating as your modem and as a source of Wi-Fi?

If no settings were changed on the T-Mobile Router, such as enabling Bridge Mode or IP Passthrough Mode, then the Decos would need to be configured in AP mode. If possible try enabling Bridge Mode, which will disable the wireless and routing functionality of the T-Mobile Gateway, essentially turning it into a modem.

There should only ever be one router in your network, as the router is the device assigning addresses and routing traffic. Having two routers on your network would create a Double NAT situation and could cause a slowdown in performance. The disconnects would also be caused by this, as traffic could be lost when rerouted through both routers. 

  @jazzman831,

So in AP mode, as you have probably discovered, you have access to a lot fewer settings: The difference Between Deco in Router Mode and AP Mode

Those two disconnects from the PC are likely the DHCP lease expiring and the computer renewing the lease. But fixing the Dual NAT should drastically improve the stability of the network.

I would first start with triggering a network optimization for your Deco network, as this will help renegotiate now that the settings have been changed. Then try forgetting and reconnecting to the network on your devices - as they may be using older settings that are slowing the connection.

I would highly recommend checking the WIRED speeds when connected to the Main Node, vs the Satellite Nodes as this would indicate if the slowdown is on the client side or within the network.

From there, there may be settings available to you for beamforming and fast roaming. If your devices support the technology you should see a much greater range.

Lastly, I would recommend either swapping nodes or providing a different power source, as the 5GHz should be able to reach slightly further than what you are saying. For the nodes that are 'potentially' causing a slowdown, try moving the node to your deadzone, as it may be causing interference or too many wireless hops where it currently is- which would cause the slowing.

All settings that would help route a more powerful connection to the devices would be on the T-Mobile router, I would check to see if there are any QoS settings on your T-Mobile Router that may be reserving or limiting the bandwidth. If there are, try assigning the Deco as a priority device. What T-Mobile Gateway are you using, so that I may look at the documentation for it?

  @jazzman831,

Looking around, there is some pretty similar experiences for your Gateway. As it is a 5G Gateway, it is also subject to more interference - try taking note of the times you see the far slower speeds to see if it happens during the 'Rush Hour' for internet activity. 

I would try and also run a speed test directly from the Gateway to see if they are similar to what you are receiving when connected to the main node. Depending on the results, settings may be configured on the gateway to help, but you would need to visit other forums or subreddits for recommended settings. If they are different, then changes could be made to the Deco to get the full bandwidth