OK, got things resolved: I had two TIU's to update to 5.0; a Rev G and a Rev L. The Rev L wasn't a problem on Windows 10 with the USB cable but couldn't find the serial port (for the Rev G, USB to serial) even with downloaded drivers. What I did was take my old laptop with Windows 7 and load Ver 5.0 on it: loaded 5.0 fine with the USB to serial cable.
Special note to Barry: "Saved by the Companion....." I had problems loading the 5.0 software on both my remotes. got 20 messages to hold the power button down......let it go....hold it down....let it go....... Read the loading remotes section in the Companion which told me to check the cable to make sure it had 4 wires; sure enough the handset cable I was using had two! I swapped it out for a 4 wire one and had no problem loading the remotes. Thank you Barry....
Thanks to everyone else as well, I have to check out the serial driver issue again on my Windows 10 laptop....
Mike