Extremely slow Wi-Fi- SBG8300

The SBG8300 is an AC1900 device. Thats what you replaced. why are you expecting faster speeds from the same specs? 

What device are you testing with? 

What is inbetween the router and the testing device? Keep in mind certain materials block wifi better than others. If you’re home is brick, plaster lathe, got foil lined insulation, etc, you’ll see faster drop off’s in speed versus standard wood/sheetrock

didn’t know they’re the same kind of device.  mostly standard wood/sheetrock between router and testing location.  specs are 1800 sq ft coverage for night hawk and 2800 sq ft for SBG8300.  So I would definitely expect better signal strength and speed from SBG8300.  my test was done with the exact same setup, same locations for router and testing device.

The “up to ****ft” coverage is always over inflated and varies by manufacturer. 

I’d return the device if the old one wasn’t bad. Your only real upgrade from going from one to the next was the SBG8300 has a better internal modem. But you won’t see that performance over wifi. 

If it was me, I’d upgrade to either something from the AX generation or I’d upgrade to a wireless mesh system. You could use the old modem/router and just put it in modem only mode. Then connect the mesh system to it and have better coverage. 

Thanks @plemans .  I switched back to my old nighthawk.  Now I’m getting a little less than 300mbps at the router and 170mbps at 25 ft.  This is far better coverage than the SBG8300, no wifi dead zones anymore.  I’ll try AX next.