I'm with Vodafone as well, the modem they supply is complete pants, but you also need it to complain about speed issues
I now have maximum discount on my sad connection 39Mb use to be near 60Mb, now on last working port (sort of!) in the cab.
So I bought a Fritzbox 7590 to replace the THG3000.... so much better, no lag stutter latency now
a bit over kill but currently surfing/gaming on my TP Link RE450 wifi bridge at 975Mb / 5Ghz band.
I can also change/split WiFi channels and renumber them!, try that on the Vodafone unit. Ok so stats are limited on Fritzbox.
Have you noticed the THG3000 has a habit of lowering the Down stream Snr? mine kept taking it down to 3.5db on my ECI line, a bit of artificial mangement to get highest speeds but caused no end of problems on BBC iplayer/Netflix
Fritxbox is now on 6db sooo much better and for similar money that the XMG sells for.