Packet loss usually relates to the service provided and a signal problem. Not usually the modem. I wouldn't purchase a new modem at all. You can swap one out free of charge at any BRC walk in center.
If you don't have the time to swap it out have a tech come out and check the line. If the modem is owned by you then BRC isn't on the hook to come out and replace it for you. So you may be charged for a service call if the technician comes out and doesn't find anything wrong.
You are in a tough spot if you actually own the modem yourself. I'm not sure if you can get another modem from BRC if you own yours. If you want to avoid a service charge then I would consider switching out the modem. If BRC owns the modem just demand a technician to come out and they should figure out if its a signal problem or a modem issue.
You should log into the modems diagnostic page and see if the signal levels are within spec.
»Comcast High Speed Internet FAQ
»What should my Signal Levels be?
Usually you can get into your cable modem by entering into the address bar of your web browser: 192.168.100.1 or the default gateway found in the details portion of your local area network connection.
However, those signal levels don't give the entire picture if there is a signal fault. The technicians have specialized equipment that can see beyond just the signal levels provided by a modem or cable box.