lostmichigan.... This may seem like a longshot but, I recently ran into a similar problem with my home modem connection (both my work laptop & my personal tower PC), though not WiFi related. My modem connection speeds ranged from no connection to 49.2 kbps (previous normal was constant at 45 to 49.2 kbps, resp.) and were erratic with every connection attempt through 2 different ISP's. Working w/ my ISP, software/hardware vendors, phone company were fruitless. Later, one of my service technicians made a suggestion that worked.
I connect each computer at different locations at my home (never have had a problem at work w/ the laptop, which is a WiFi connection, only at home w/ the modem, and the tower is a fixed installation at home). My problem turned out to be an internal phone line hardwire (terminal) connection. I found no loose terminal connections when I physically "jiggled" each and every phone line connection but that seems to have solved the problem. The connection problem has not recurred since (several weeks now). I suspect that one of the connections was sufficiently corroded that my jiggling created a clean connection.
Consider also that if you live in an area of the U.S. or Europe that has been hit in recent weeks with unusually high ambient temperatures and/or humidity, materials used for wiring terminations (Aluminum, Copper, etc.) are subject to corrosion, though often visually unnoticeable. Consider the static of an old radio whose tuner has never been cleaned. Even slightly corroded terminations can fail a connection or cause sufficient "noise" in the line to prevent a connection to your ISP. I deal regularly with similar issues in my business.
My advice, as I give to my customers, is to leave no stone unturned. Check your software, PC hardware, wiring, terminations, etc. Never assume
Keep the faith....ProEd