The first thing I would do, set with the default SNRM, is to note the sync speed with the modem configured for: (1) ADSL (2) ADSL2 and finally (3) ADSL2+
Once those results have been obtained, then set the modem to use the best mode. I'll hazard a guess that
ADSL2 will probably be the one to use.
My next step would be to switch off and disconnect the modem from the DSL for a minimum period of overnight, 24 hours might be better. Reconnect and power it up during the "good" daylight hours -- 1100 to 1300 hours -- and let it run for a
week without any "fiddling" or "adjustments". Keep a record of all the statistics gathered over that week.
Now make one (and only one change), perform a warm re-boot and let is run for the next week, etc.
"Slowly, slowly" should be your watch-word pair.