I
knew ordering a stand alone LAN card would solve my problem! It hasn't arrived yet, but after not connecting once yesterday despite a dozen variants of uninstall/reboot/reinstall... today, all is well. This morning did a "Repair" install of the Realtek LAN drivers without uninstalling first, rebooted and ta-da! Several Restarts and Shutdowns later, still working like a champ. Could this be it? Hope springs eternal, eh?
DM, I thought about reinstalling again from scratch but given I'd done that three times on two separate motherboards the probability didn't seem high enough to justify the day of reinstallation pain that it would cause, so ordered the LAN card. $12 seems little enough if it saves a day of effort. And just maybe I'll get to return it anyway.
Will keep you posted.