Nighthawk(R) X4S R7800 Only Getting 35 Mbps

[Thisismyaccount]

My router can't seem to detect more than 35 Mbps for the bandwidth:

Above is what shows up under Attached Devices when I login to the router. All of my tests, whether they are WiFi in another room, WiFi right next to it, or Cat5 cable directly to it (6 ft cable) all seem to max out around ~35 Mbps for download speed. 

When I plug my computer directly into the modem (with the same cable that connects to the router) I get 300 Mbps. 

I've tried adjusting the channels and several other settings and nothing seems to make a difference. It seems like it should be recognizing the 300 Mpbs on this Attached Devices screen.

Also, I have disabled both of my guest networks - so now it is just the 2.4 Ghz and 5 Ghz networks (with Smart Connect enabled to switch between 2.4Ghz and 5Ghz). I originally had Smart Connect disabled and had two separate networks, but that also had the same bandwidth when I tested it.

I have restarted the router as well. I just haven't done a factory reset yet.

[plemans]

what modem/gateway is it? 

what firmware version are you on? 

Have you tried a simple factory reset and manual reinstall of the router (not from a backup configuration)?

[Thisismyaccount]

I am on firmware version V1.0.2.78

The modem is an ARRIS SURFboard SB6190 DOCSIS 3.0: https://smile.amazon.com/gp/product/B016PE1X5K/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 

I have not yet done a factory reset. Might try that later today.