@David-TP  Yes the Deco hooked with the Ethernet cable shows Ethernet in the app. As for the speeds Ill refer to my original message which I stated them, im testing on my Phone.

I use my phone connected to the Deco Wifi and the speed test is the same, I also used the Deco app and its the same 500-600mbps. If I walk to where the other decos are, either the WIFI one of the one hooked with a ethernet cable directly to the main deco, my speed is 10mbps on the wired one and 75mbps or so on the WIFI one (which is closer to the main Deco) on all tests.

  @David-TP 

Turning 2.4 off didnt change anything. I have a Samsung Galaxy S21 and am using the speed test in the Deco App and multiple tests online and they are all consistent with each other.

  @Cue555 

It is possible you have two separate issues with your Satellite Decos.

The one that is Ethernet wired might have negotiated 10Mbps over Ethernet connection, instead of 100Mbps or gigabit. This is unusual, but there is no other way to explain why are you getting just 10Mbps - when everything is correct, from wired Satellite Deco you should be getting same speed as from Main Deco.

To check that theory, connect your desktop computer with Ethernet cable to that wired Satellite Deco, and run Ookla speed test on computer. If that speed test returns 10Mbps, something is wrong with your Ethernet wiring. 

For Satellite Deco that is wireless, it might have been placed too far from Main Deco. Check what it shows under Signal Source for that Satellite Deco, make screenshot and post in reply for me and @David-TP to see.

With proper placement of wireless Satellite Deco and everything else properly working, you should expect to see at least 250-300Mbps from wireless device connected to Satellite Deco, if your Main Deco delivers 500-600Mbps.

Also, for that Satellite Deco you can run same test as above, which is connecting desktop to it by Ethernet cable, running Ookla speed test on desktop. Please share the result: this test will report speed of WiFi connection between Satellite Deco and Main Deco.

  @Alexandre. Not sure what you mean? I cant hook my computer to just the deco, then I would have no internet to test speed with?

The sattelite deco is only about 30 feet away upstairs, and this set is supposed to work in a 6000 sq foot house I think, which mine is nowhere near. Signal strength shows 2 bars.

  @Cue555 

Wired Satellite Deco

Please see this document for general topics in regard to wiring Satellite Deco: General questions about Ethernet Backhaul feature on your Deco

I expected you have standard wiring of Satellite Deco, which could be the following:

Also, another option is quite common:

Finally, this can work, too, for Deco in Access Point mode:

Is your home network set like one of those? If yes, you can just connect your PC to an available Ethernet port of Satellite Deco. Then, you can run Ookla speed test on desktop PC, as I asked.

In case you have Satellite Deco connected differently, please draw the diagram for better understanding of what you have.

Wireless Satellite Deco

"This set is supposed to work in a 6000 sq foot house" - 6,500 sq. ft. actually, but you missed multiple things marketing does not want you to notice. One is "up to," another one is not having obstacles like walls and Wi-Fi interference from household appliances and neighbors' home networks, if you ask for superior speeds. 

Also, note how you are promised sq. ft. coverage but not the speed. 75Mbps from Satellite Deco does mean you have WiFi coverage. As they promised. 

For wireless Satellite Deco, its placement is important. The speed it can deliver to wireless devices can not exceed speed Satellite Deco gets from Main Deco. This is the purpose of a test I suggested: with PC connected to Satellite Deco by Ethernet cable you can find what is the speed between Main Deco and Satellite Deco.

For wireless Satellite Deco, the best placement is approximately in the middle between Main Deco and where you have your wireless devices. If, for example, you want very good WiFi speeds in Master Bedroom, you should not be placing wireless Satellite Deco in Master Bedroom. 

  @Alexandre. 

Yes, I have mine setup like the first picture.

 I have found out something is wrong with my network cable, if I disconnect it, the speed test goes to 60-75mbps even though the deco is pretty far away from the main one, probably 100 feet and in another building on the second floor. I think ill leave it like this for now though. Not sure whats up with the cable, with my tester a few times one direction it showed as a crossover connection, then tested from the other direction it tested good, then would test good on both ends the next time. Ill have to put new connectors on both ends and test again.