When you said that SBC (now AT&T) has reported no conectivity issues, do you know if they were looking at the PHYSICAL line testing, or did they look at the Logical layer to see if there was any congestion on the line? If the issue persists, call up the DSL department, and ask them to look at the amount of traffic on the link. I am thinking that chances are good that it will be alot of traffic causing this issue.