Weirdly I have a similar problem
Switched from an Asus router/modem with Mediatek chipset to a Draytek Vigor 2760 with Lantiq chipset
Generally speaking is better as my line is now on fastpath, but i noticed my upload speed dropped from 13mbit to 10mbit
Did you try messing with the modem code? Mine is using the stock BT firmware
I did a while back try messing with the modem code.... but it didn't enhance anything.
Bit of an update, as I mentioned before I have gone back to the EE Smart Hub that EE originally sent me... but I never used as I had the Vigor130. This way I can then complain to EE technical support... if I can identify it's a problem at their end.
Interestingly, after connecting the Smart Hub, over the lasy few days my Download speed has gone up considerably...was around 60Mbps and now it's reaching nearly 70Mbps.
Sadly the upload speed hasn't really changed that much, but it is higher by about 0.5Mbps
Stats are now
Data rate:8.96 Mbps / 74.00 Mbps
Maximum data rate:8.96 Mbps / 91.58 Mbps
Noise margin (up/down):5.7 / 10.7
Line attenuation (up/down):23.2 / 17.5
Signal attenuation (up/down):23.4 / 17.5
So maybe with time the upload speed will creep up even further.
It is however loosing sync about once a day, but this is in the early hours of the morning and so, I'm told, could be openreach doing maintenance.
I'll leave it for a few more days and see if it settles down or keeps loosing sync.