I have the same. Give it a couple of days. You may see sync speed improve like magic for no reason. That is what happened to me. I think it might be something to do with the DSLAM you are connected to.
Sometimes what you don't get is a blessing in disguise!
The guys at Iconz logged a fault with Chorus earlier this week after I've provided them with the detailed diagnostic of the new router (and it being able to give me attainable sync speeds of up to 17000ish for downstream but the router still consistently syncing at 8158).
Apparently Chorus initially came back to them saying that my 8158 is well inside of the specs, blablabla. Another try of the Iconz guys resulted in a certain Chorus person then tweaking my profile a bit further so that I'm actually syncing at 14000ish downstream now:
Down Up SNR (dB): 7.1 15.5 Attn(dB): 25.0 10.1 Pwr(dBm): 19.0 12.4 Max(Kbps): 17692 945 Rate (Kbps): 14057 945
Speedtest.net up to the Worldnet server in AKL gives me around 11.5-12Mbps now (as opposed to the 6.5ish Mbps it returned before).