The best way to check your connection speed is to follow
this advice. [There appears to be a problem with that link - it should take you to the DG834G section of the page, but if it takes you to the bottom of the page instead you can scroll up to the DG834g section.]
A high noise margin is good from the point of stability. What has probably happened is that your recent problems resulted in your target noise margin being raised to make the connection more stable. If the interference problems are now over and your connection is now stable, the automatic processes should lower your target noise margin in steps over a period of weeks, but exactly how this process works doesn't seem to be documented publicly.
I'm afraid that there isn't a version of the DMT tool which works with DG834Gv2.
