Dug, I tried MANY things ... but to keep it short, I ended up using CXXXXXXX-A for host name (my Dlink DI-614+ doesn't have both computer and domain name), and cloned my main PC's MAC address for the router. I think one possible source of my problems is that I switched from a Linksys router a week ago. Maybe ATT was "used to" the Linksys' MAC address.
Service has been spotty for the last 2 weeks or so, but was really bad last couple of days. It is up again, now for almost 24 hours, so like I said, I am leaving it alone until it goes down again . I will definitely call ATT up now if I have problems, thanks kgraeme.