So what Comcast can do is call them up and talk to a tech support jerk off. They can test the packet loss directly from their servers to your (their) cable modem. If there is packet loss, then it's generally on their end. Depending on where you live, Comcast has probably over subscribed the bandwidth wired to your neighborhood or complex. This is completely 100% their responsibility if that's the case. However, since they've been out to your place multiple times and they claim the cable modem is functioning properly, I can only assume there is problems between your computer and router.
First, however, you need to call Comcast to *ensure* the do a ping/packet loss test from their server (local hub) to your residence. If this is fine then we can troubleshoot this further.
Is your router wireless? Is your packet loss still continuing with a wired connection from your computer to your router? What are the exact specs of the computer you are using? How exactly is your network set up? Is the surfboard connected directly to your computer? If so, is this a USB or Ethernet connection? If Ethernet, is this connected to the back of your computer next to other ports like USB, firewire, etc.(motherboard) or is it connected towards the bottom of your computer (add-on card)? How old is the computer you are using? Describe to me exactly when and how long the packet loss sessions last -- 1 time, 1 minutes, 5 minutes, 10 minutes, half hour, or more? Do these occur at the same time of night every night? Only on weekends or certain days? Have you checked/tested the cord/connection between your router and your computer? Is there anyone else using your network whether wired or wireless? Have you ever called Comcast at the exact same time the problem was occurring?
Okay thats alot of questions i will try to answer them the best i can if i miss anything sorry ill try to get more info once im home for computer specs.
1) My computer is ethernet wired to the router
2) I have these random disconnects from my internet throughout the day and the packet loss is constant.
3) I have myself on my wired connection and my roommate on X-Box live in the basement on wireless.
4) When i called Comcast they told me that that don't have that same packet loss on their side.
5) I had the tech call while he was here when i showed him the ping.test and they said it was fine on their end, I was getting 50% packet loss even right after the house was totally rewired while the tech was there.
6) The disconnects are at random times.
7) I have called they right when my connection drops but they can't id the problem and always tell me that they will have to send a tech out.

The packet loss is constant so their isn't a time when my connections is not losing 50%+ packets at all time.
9) my computer is about 18 months old and my etherner cable is fine i swapped them out brought new ones nothing has help... Also its plugged in ethernet slot towards the middle of the tower, but have tried any slot available no difference there.