If you have the ability, get a DSL splitter and put that at the box. Split the dsl line and run that directly to your modems. Don't let it get on the inside wiring at all. I've done that in two places I've lived, and I've doubled my effective speed each time. The splitters are like $15 or $20 online.

It may or may not be the issue you are having, but it totally removes the inside wiring issue from it. Considering how most homes are wired.....