I just switched from High Speed 25 to Internet 150 today and got the new Cisco DPC3848V. Immediately after installation, I noticed 2 major problems:
1. Really high latency while connecting directly to the modem with a wired connection, when no internet traffic going on at the same time, as you can see from the attachment. Sometimes it goes as high as 400ms. My old modem never had this issue.
2. Port forwarding on the new modem/router doesn't work at all, I tested with a web server and a TCP tool, both of them works fine when connecting with a LAN address, but don't work at all when connecting with my external IP. No matter how many times I reboot all my network devices. Again, my old modem never had any issue with the exact same setup.
I spent a long time trying to figure out a solution but with no luck. The latency is not a problem when browsing but it's going to be a pain when playing online games, and port forwarding is a must have in order to play with my friends.