5Ghz wifi drops every evening

Every evening at about 5:30-6:30, my 5 ghz wifi drops out. The 5Ghz network occasionally completely disappears from the list of available networks durng this time. My Xi6 wireless STB goes completely off line, and  and all connected computers/tablets/cell phones also drop. Pings to any site jump to 500-1,000 ms, and speeds drop from 200 Mbps to about 2-5! When I reboot, things return to normal until the next evening when the cycle repeats itself. This started about 1 week ago.  I have the TG3482G gateway.  All upstream and downstream s/n and power levels are within normal specs. Thanks in advance for any help....