Help, why is my upload speed so slow randomly?

Help, why is my upload speed so slow randomly?  I've had this issue with my old internet package with an older modem.  After upgrading to gigablast speed with the panoramic modem the first 10 min's after installing showed an upload speed of 34 Mbps and then randomly my internet would slow down and my upload speed would drop to below 0.9 Mbps.  This speed is through my hard wired main pc through an ethernet cable and also my wifi speeds are slow.  I have the unlimited data package so I know I'm not data capped either.  It's been nothing but frustrating.  Any help or suggestion?