AT&T Service Issue
I have the same problem of my connection slowing down to almost nothing every night. While I haven't found a solution yet I have filed complaints everywhere I could think of to file. These are online complaints and only take a few minutes each to do. I filed complaints with:
Texas Attorney General
Texas Public Utility Commission
and the Chicago BBB (my bill has a Carol Stream, IL address)
I will be writing all my state and federal reps and might even send an email to the President. I do believe we just spent a lot of tax payer's money on internet connectivity.
I will also be sending copies of all my complaints to any news outlet that will take them. It is just ridiculous that this is happening all over the place and AT&T refuses to do anything.
Make noise, they are the largest and most profitable communications company in the world, they can afford to fix their issues.