U-verse Internet down every night at 11:30PM to 12:30AM...Then Back UP again around 7:00AM

I have had U-verse internet now for several years. Started with 1.5 MBPS plan and eventually was able to get 3MBPS and have now been on the 6MBPS for a few years. I have always bragged on my internet telling people "hey my internet may not be the speediest, but it NEVER goes down". I live in rural area and out here that is definitely something you can brag about :). ATT has always provided me with a super stable connection and my speeds have always been 6.3 to 6.8 mbps download and .60 to .80 mbps upload. About 8 weeks ago my internet went down around 11PM EST. Naturally I was not alarmed because every two to three months my internet would go down for about 30 minutes to an hour late at night which I assumed was maintenance. However, my modem never would sync up the rest of the night. About 7AM the next morning my internet was back up and stayed up throughout the day. 11:30 PM that night its back down again, never syncs up, then Back UP again at 7AM the next day. At this point I knew something was wrong. During the time that my modem was down at night, the line status would sync up, it would connect for about 30 seconds, then go back down again (repeats all night). Every time it would sync up my Maximum attainable download would be 9500KBPS to 10000KBPS and right at 1MBPS upload. I also noticed my modem taking FEC errors even during the day that would reach into the millions. ATT phone tech said that they saw a problem in the home and they sent out Technician #1. Tech 1 replaced my modem because he thought it could have taken a lightening hit. Of course this was 5PM in the evening so the internet syncs up just fine. That night 11PM my internet is down again, and back up the next morning at 7AM. I called ATT again they proceeded to send out Tech #2. Tech 2 tested the lines, replaced the modem a Second time with a different model and also cut a bridge tap off the line. Internet goes down again that night about Midnight and comes back up again at 7AM. Also I want to make it known that the whole time my internet is synced up during the day my speeds are exactly what they are supposed to be as well as my ping neither one falters the slightest bit. This was on a Sunday so I was planning to call Monday morning however that night it never went down. The modem was still taking extreme amounts of errors, more than I have ever had, but it never disconnected. I thought maybe the night that Tech 2 left they may have just performed coicidental maintenance. Internet works flawlessly day and night for about 9 days, then its down again at night, and back up in the early morning. That goes on for about 2 days and I decided to call ATT back yet again. The phone tech says they can see problems on the modem so they send out Tech #3 that afternoon. Tech 3 replaces the modem yet again and tells me that I need to back my speed down to 3MBPS plan. I ask him why would my internet be working perfect on 6MBPS for 4 years then one night just decide to stop working, and ONLY stop working at NIGHT. I agree to back my plan down because at this point I just want a stable connection. That night my internet is back down again and then up again the next morning, same old problem. So after a couple days of the same problem I changed my plan back to the 6MBPS because I need all 6MBPS considering the high amount of internet activity in my home and my internet has been working fine for the past 8 to 10 days, now the problem has started again, down at night, PERFECT during the day. I am really quite frustrated and I haven't called ATT back yet because the technicians seem to have no clue what is going on... If someone can please give me any ideas as to why this might be happening ONLY AT NIGHT, help me, or give me a contact of someone at ATT that would be willing to RESOLVE this problem rather than just simply replacing the modem please help! I am desperate at this point! I take college courses online and unstable internet just doesn't cut it in my home. Especially since ATT UVerse has been SOOO great and awesome for the past four years. I just want my stable connection back.

Mike