Have you been to the Comcast store to exchange your modem for another one? Thats probably something that they will want to do. Might as well save some time and do it yourself so you can tell them you have already done it.
Actually I had the modem switched out the first week of my service. Comcast technician did come today and I was right! It was their line coming into the townhome, which should be fixed by Thursday by the latest. Did not have to pay for the service call, at least the technician didn't say anything.
Well I thought the problem had been fixed...apparently a second technician did come out and I noticed a spike in the speed on Wed...but then Thursday and today came and it was right back to being slow again. So I called Comcast again and they're gonna send somebody else out next Friday to check the lines again...this is starting to frustrate me. The wife was trying to watch Heroes online last night and she gave up because it kept stopping every few seconds. What the hell am I paying for?