This is an update to the last time I posted about my DSL modem
The old modem finally broke, so I had to replace it. The “Actiontec C1000A” that I got from CenturyLink had a selection in the WAN setup for “Transparent Bridging”. With this simple option, my Tomato router was able to connect.
I also disabled the wireless on that modem, so that it just does DSL decoding. It has the ability to do VDSL, which I might upgrade to later.