just a suggestion but do you have one of those charging docking stations you can place your controllers into to charge up the batteries?
I was having the same issues a few months ago with my sons xbox live. Was working fine for a year and then it started playing up all the time. Kept logging out of live. Reset router, changed settings, etc etc.... nothing cured it.
We, sorry, father christmas bought my son one of those controller docking stations and we found out that was interfering with the wireless signal from my router to my sons bedroom. i unplugged it and live has been working 100% fine ever since. i have since plugged the station back into his xbox but moved it as far away from his box as possible and he hasnt once had problems with his live.
i had the idea from a neighbour who was having issues and it turned out their problem was caused by a baby monitor interfering with the wifi signal.
maybe worth having a look around for any electrical items that could be causing interference??