PACE 5268 -- Wifi Woes with 5GHZ -- Are these boxes junk?

We just got fiber and they installed a new 5268 because of problems we were having with the 5GHZ network disappearing.   Everything has been great for 6 days.   Today I went to use my Fire stick and it could not connect to 5GHZ.   Since the stick was new, I assumed it must be something in the stick.  Then my wife went to use her smart TV which had been working fine.   It wouldn't connect.   Her Echo Dot also went out.   I asked them to try a Roku in another room that was also connected to 5GHZ.   Also dead.   Meanwhile our computers and smartphones seem to be connecting to 5GHZ fine (although I'm not streaming, so maybe that's the difference).   

I'm frustrated because we seemed to have much more consistent speeds on both 2.4 GHZ with our gateway we had several months ago.  The 5GHZ network seems to be great for a few days and then complete goes to pot.   The 2.4GHZ on the 5268 seems to send very inconsistent speeds and is much slower than the 5GHZ for my fiber wifi.   

I don't know what to do, especially if my only option is another 5268 that's gonna fail the same way.   Has anyone had better luck with a new router run through the 5268?   Are there easy instructions for installing one with U-verse Phone and TV connected?   Can anyone recommend a reliable WIFI router?