Solved. I had turned off NAT Boost in my router so I could log traffic statistics. Apparently that slows down everything going through the router. Turned traffic statistics off and NAT Boost back on and I am back. Thanks to Cox Support via email, for guiding me in figuring this out.
Apparently so. FYI TP-Link 1200 AC -> Arris TM 3402A. Whoda Thunk? Plan is now 250/10 with automatic speed increases from Cox on the premier plan. Been that way since 1999 when it was 50. BTW, I never noticed the speed drop in my daily use until I did a speed test just for something to do.