When it starts misbehaving it may be worth checking errors on your DSL connection just for the sake of elimination.
CRCs & Err Secs can cause the symptoms you describe in your first post.
However I'm not quite certain if you meant you get periods were its like that. You said in the first post you were unable to get a stable test, yet the last 2 whilst jittery dont appear to bad.
List of some possible causes;
- Congestion
- Network traffic
- Line Errors ~ CRCs
- MTU
That slow to rise green line also reminds me of an issue that I had a few years back on one of my machines with nVidia drivers & Nstream. :/