Network intermittently dropping/extremely slow speeds when downloading large files

I regularly download large files (from steam, computer games) and when downloading at the relatively high expected speeds (I have 1gb/s internet) every few minutes the internet speed will drop to 0 and my windows PC will show 'no internet connection.' Then after a minute or so it will resume downloading at the expected speed, rinse and repeat.

This all started after I got a new (white) modem from Xfinity; truth be told I don't know where to begin. Any help would be appreciated! 

Thank you!