I have a Arris SB6141 which is rated at 343Mbps. This is happening with and without the router by the way. The ethernet cable is a Cat5e that's 6 foot long. My router is a ASUS RT-N66U Gigabit Router, both of the these items are only 2-3 years old. The only thing that changed was my Spectrum internet plan went from 100/10 to 400/20. I know I shouldn't expect 400Mbps with the modem but I should at least get in the low 300's right ?