Downstream Atten. at 300kHz: 69.3 dB
I'd speculate that the attenuation is the root of your problems, it means that your line is so long that only the tiniest signal levels are present at your router. You are lucky DSL works at all.
If that figure is accurate then it suggests that your normal level of background electrical noise must be very low indeed, in order for DSL to function, even as well as it does. But it;s possible that when even the slightest levels of interference arise, at a level that would just be 'normal' for most people, they are enough to swamp your tiny signal and will cause the connection to drop.
I'd suggest two things....
First, keep an eye on that downstream attenuation figure to make sure it's accurate. If may drift around by as much one dB or so, but if it changes a lot (say, more than 5 or 10dB) then it suggests a wiring fault in which case getting it fixed would clearly improve things. Observe, for example, whether it is affected by lifting a phone off-hook (it shouldn't be). Also, that attenuation suggests a distance of perhaps 5km from the exchange... is that in keeping with what you expect?
Assuming the attenuation is correct and constant, you may just have to make the most of what you have. It is vitally important, with such a long line, that you do all you can to optimise your wiring. Have you already checked out the guidance at
http://www.kitz.co.uk/adsl/socket.htm ?
