Speed flucuation and gateway/app connection

I feel certain my gateway is in the best location I can find it’s a FAST 5688W.

When I first got it, speeds flucuated from 400 down to 40 mbps.  If it got low I connected to the gateway with the app and did a reboot.  When the reboot was finished I was always back up to 300-400 mbps.  When I logged in to the interenet I was one tmobile connection.
 

One day the internet went out completely for 48 hours (cut cable under a road they told me).  Since that time, I still get 40-400 mbps most of the time, but if I reboot the gateway with the app I 1) usually get my fast reconnection, but when I try to connect to the gateway, it acts like I have no internet connection and says tap to check connection.  When I do, it says connected, but it will not take me to the main tmobile app screen.  Instead, it tells me to power down and power back up.

Then last night, speed was slow.  So I rebooted and even though it came back and said connected, using speedtest.net started at 1-2 mbps and increased to about 25 mbps at the end of the test, but intenet navigation was dismally slow. 

Usually when reboot speeds are slow I'm on N41.  If it switches to N71, that's when speeds go higher.

It just seem like the gateway could be smart enough to continually seek the best signal.