@wifiMeshNewbie 

Disable the 2.4G network to force 5G connection. If you are testing while away when close to a satellite node, try wiring the Deco units together which will provide a faster connection compared to Wi-Fi.

@Tony 

I have a number of old alexa and nest that is only on 2.4GHZ so this will not work. I tried an alternative with the Guest network at 5GHZ leaving the main with both 2.4GHZ and 5GHZ enabled, but the 5G speed is only available at close range to the router. I am talking less than 10 ft.

 What is the operating mode you setup? Router or Access Point, and what's the difference in wifi performance. It's just the wifi is extremely slow even with a strong signal.

@wifiMeshNewbie 

Both set up modes should be similar, but in router mode, all satellite nodes would need to connect to the main router, wherein AP mode you can have multiple nodes wired to the main router.

So your 5G speed is fine, you just have issues when a device is connected to the 2.4G?

@wifiMeshNewbie So here is my take. 5G vs 2.5 -- 5G is faster but has shorter range, that is the nature of bandwidth nothing can be done about that except to increase number of repeaters to boost the signal. 5G does not penetrate but gives more wifi bandwidth.

2.5 is the opposite - longer range but slower speed.

Few other things to consider.

Just bcaz your ISP is providing a 1G wired connection it does not mean the router will broadcast 1G wifi. the router may not be capable of 1G wifi but throwing max speed which is less the 1G.

which mean the wifi is not broken but reached its limit.

for a true test use wired connection out of main deco and does that produce 1G speed, if YES then everything is working as expected. If the wifi is super slow then YES the issue still persists.

hope this helps