Major Internet Speed Issue

I have recently upgraded my packages across the board from 5 MBPS to 50 MBPS but my speed continues to cap at 8 MBPS and that's on a good day I have the "latest and greatest" as far as router/modems and they claim to be able to handle exponentially more than what I am signed up for but I Still cant get better than 8 MBPS at any time. Please Help