DGN200 and ADSL

Hi, I just replaced my very old USR modem router with a new DGN200: I have a problem I can not solve:
At the same Wireless Network Connection Speed (11.0 Mbps) the old USR in ADSL speed test give 4 Mb in download while DGN200 even after repeated settings only. 0.8 Mb.
No problem, however, if connected in ethernet.
Thanks:confused: