Hi, and welcome to the forums!
Here's an unofficial answer for you:
It's possible that your sync has lowered due to your Target SNR being raised from the default 6db.
For each 3db your Target SNR raises you lose approx. 750kbps of speed - this is BT's systems attempting to stabilise your line if they think there is a problem - possibly caused by your earlier faulty router.
In theory if your line remains stable this will reduce automatically - but sometimes this doesn't always go as planned.
If you can post your line stats: Sync/Attenuation/SNR this will allow people to judge where the problem might be.
More details on understanding
ADSL Max
Hmmm...