Mystery solved...

After six and a half years of faithful service, my modem was dying, slowly. New modem, no problem. Why did I not recognize the symptoms? My last modem was fried by lightening. Instant death. For future reference, mine had a good lifespan. Computers change, the internet changes, and modems need to be periodically replaced (5-6 years) to keep pace. Fascinating. The tech was great, answered all my questions, listened, and never made me feel silly.

I noticed that the cable between my computer and the modem was the one I've been using and the new one was still in the box. I called my sister and asked if I should trade out the old one for the new one, keeping the new with the new, and saving the old for "just in case." She agreed with me, but then I probably learned it from her. :-)