Before you do anything else, change that Ethernet cable that's going between your new modem and the next device!! As I mentioned, when you see speeds max out around 90Mbps that is almost always an indicator of Ethernet link speed that's 100M instead of 1G. If you change that Ethernet cable and it doesn't help, try yet another one! As I mentioned, a brand new Cat 6 2-foot-long cable refused to link at 1G no matter what I tried. It seems like the Comcast modems might be more sensitive than the old ones when it comes to link speed.