Thanks, Alex!
I'm able to submit with my laptop using a hotspot down the street.
I've narrowed it down to my ISP since I was able to submit to GG's link list for a complete year when I had AOL DSL using the same router. My switch to SBC is what brought about my problems with site submissions.
I tried a different DSL modem since I ran out of ideas.
What should I say to my ISP when I contact tech support?