Slow speeds - Motorola Model MB7420

Hi, Comcast, 

For the past few months I have experienced slow speeds and frequent signal drops. I used a cable modem and separate wireless router. I have had the same tech for 10yrs without issue, though recently replaced both the cable modem and router to see if I could fix the internet speed issue. It did not. Comcast ran several virtual tests and eventually sent a tech to inspect my connection and recorded 1300mbs from the coaxial cable. The tech said my new cable modem is likely the issue, but could not confirm w/o me switching to using a Comcast cable modem via rental plan. This seems odd, so hoping a tech here can help verify this advice or share alternative ideas. Details below:

- 400mbs Comcast plan 

- Speed tests result in 10-12/mbs (performed via wireless connection) 

- Lights on cable modem show 'online' but 'ethernet' light is intermittent 

- Tested multiple ethernet cables from modem to wireless router 

- Tested 2 different cable modems and wireless routers (both are Motorola cable modems, Linksys routers)