Go to 192.168.100.1 in an internet browser and post screenshots of your signal levels and event log. If it asks for a password try admin/admin admin/password admin/motorola
You could try taking the modem outside to the demarc where he tested it eliminating all of the house wiring. If it is still testing at a slow speed it's likely the same oversubscribed node issues 80+% of people are facing. Their nodes can only reliably service a certain amount of houses which they oversubscribed before upgrading infrastructure. Everyone is sharing a pipe and it's only so big. Have you spoken to your neighbors to see if they also have the same issue?
I was having the same issue, in addition to packet loss and high jitter. They finally, after about 8 months, split my node last month. After the node split I am getting 700+Mb download/35up. Still isn't 100% though, some peak times still have packet loss and have slower speeds.
