@Bmoore 

Regarding Configuration Compatibility:
Yes, Deco supports this configuration. The Deco X55 Pro works with any standard Ethernet connection, and since your MoCA adapters provide Ethernet connectivity, there's no compatibility issue. MoCA adapters are commonly used to extend networks over coaxial cable, and Deco treats them like any other Ethernet connection.

Regarding the Slow Speed Issue:
The extremely slow speeds you're experiencing are definitely not normal. Here are troubleshooting steps to help identify and resolve the issue:

I would call your ISP and ask if they use CGNAT or public IPv4. Deco uses public IPv4 and your ISP "might" be using CGNAT. If they are using CGNAT  have them switch it to public IPv4,

If they are already using IPv4 then try the steps listed below. 

First, verify your baseline speed:
1. Use https://www.speedtest.net or the Speedtest app for accurate testing
2. Connect a PC directly to your fiber modem/interface to confirm your ISP is delivering the expected speed
3. To verify the wired speed of your Deco, connect a PC directly to the main Deco unit using a CAT5E or higher Ethernet cable

Methods to improve speed on Deco:
1. Try different Ethernet cables (CAT5E or above) and different Ethernet ports on the main Deco
2. Open the Deco app, go to MORE > ECO Mode, and ensure ECO Mode is disabled
3. Go to MORE > QoS, and ensure QoS is disabled. If you don't see an on/off switch, set it to standard and remove all priority devices
4. Go to MORE > Advanced > NAT forwarding, and disable SIP ALG and UPnP
5. Try a few different Speedtest servers, as some may yield better results

For wireless speed testing:
1. Ensure your device is connected to the nearest Deco unit
2. Make sure it's connected to the 5GHz network instead of 2.4GHz
3. Ensure no other devices are downloading or streaming during the test

Additional consideration for your setup:
Since you're using MoCA adapters, the bottleneck could potentially be in the MoCA connection itself. MoCA 2.0 adapters typically support speeds up to 1 Gbps, but actual throughput can be affected by coax cable quality, length, and splitters. You may want to verify that both HTEM5 adapters are properly paired and check their link quality indicators if available.

For more details, you can refer to this FAQ: https://www.tp-link.com/support/faq/2429/