I recently installed a TP-Link Deco XE75 mesh system in my double-story house, but I'm experiencing significant performance issues.

Here's what I'm observing:

1. When connected to the new Deco XE75 network, even when close to the main unit, my internet speed is much slower than my original network.
2. If I switch back to my old network, the speed improves significantly. 30mbps via the XE 75 vs 800mbps via the old network.
3. The system hasn't resolved the dead zones in my house as expected.

I've already tried basic troubleshooting steps including:

• Ensuring proper placement of units
• Checking for firmware updates
• Rebooting the system
• Adjusting network settings in the Deco app

What could be causing this performance degradation, and what additional steps should I take to resolve these issues? Is there a possibility of a defective unit or a configuration problem?

Additional information:

• My house is a double-story structure with thick walls
• My internet plan speed is 1000/50
   

Any insights or advanced troubleshooting steps would be greatly appreciated. Thank you!