Ok, I think I found it.
The new Router's "Firewall" is apparently useless. Having the "firewall" enabled, plus another setting, was causing 80% of traffic to be blocked.
I KNEW IT!
Anyhow, sorry about the 3 hour outage -- we should be good now.
This router is much better -- not just raw capacity (CPU, RAM) but the software is at least 1-2 levels more advanced than the old router. Many more tools and ways to monitor. All in all, I think this whole adventure was worth it.