Different modems have different sensitivity to line issues, the new one could simply be less tolerant to bad signal levels. You should definitely complain and get them to fix it, having a technician over is a good thing.
The two sensible things you can do on your end are:
1. Check the modem signal levels from its stats page. All current cable modems have a web page that you can look at and see whether the signal is within acceptable ranges, as described here: http://www.speedguide.net/faq/what-c...idered-good-78
2. You can do a couple of traceroutes to see if there is packet loss or latency issues, and how far from your modem they occur.