Sounds about right.
Why do you suspect a line problem?
You say it's syncing at 23Mbps with a line attenuation of 14dB.
Isn't 23Mbps pretty close to maximum sync anyway?
What is actually wrong and why are you playing?
ADSL2+ with BE
DL Sync around 4.8Mbps
UL Sync 1088kbps
DG834GT with DGTeam firmware