I was fortunate that the techs TWC sent out were very helpful, especially the last one. They ended up re-running the line from the curb to my service box, replacing connectors everywhere along the line (including some in the house), and following up with me. Unfortunately that did not solve the issue for me.
They recommended I pick up a TWC modem from the local service center for a few days to see if it fixed my issues (they said it would be no charge since it was for testing). So I got an SB6183, hooked it up, and everything ran great, no service dropouts. The techs were very surprised as they said the 6141 is generally more stable than the 6183.
I ended up buying a refurbished SB6183 from Walmart.com (they have them on sale from time-to-time) and haven't seen the issue since. I definitely had line issues, and I think it was a combination of both getting the line and connectors fixed along with a new modem that fixed it.
If you have time to read the novella called my forum thread here, you'll see, with the same modem in Greensboro, NC, on 50/5 internet... wait, make that three of the same SB6141 modems now.... I get the same issues, even with perfect power levels showing in the modem signals page. I get no errors or issues with two different 16-channel test modems. Clearly, the SB6141 can no longer handle the dirty signals on TWC's old hardlines.
My forum thread:
Bonded downstream channels - TWC Community Forums
I'm actually updating it this morning, as I've been using another test modem given by my TWC tech.... this time a new old stock leased Motorola SB6141, and it has the same issues as the two I had bought.
Thank you Gedd and glenvee for your comments.
My modem signals are perfect but still my download speed drops to less than 2Mbps. My usual download speed is > 50Mbps. It's only the download speed that gets bad, not a tad bit of problem with the upload speed.
Anyway, I will go ahead and buy a new modem.
I would definitely recommend at least borrowing a modem from TWC before buying a new one. It could be that your problem is very different from mine, or that, like me, you have line issues in addition to the modem problem.
I'd also recommend either posting a new thread with your signal levels as MsRaye mentioned or at least requesting a tech come out to look at your connections and levels.