Had ~250-350MBs speeds on 300MBs service, upgraded to 1GB but only getting ~35MBs!!!

I just upgraded to 1GB service with Xfinity.  Prior to this, I had whatever the 300MBs with boost package.  I would consistently get between 250-350 MBs speeds when testing with SpeedTest.  I just upgraded to Xfinity 1GB and now I am getting speeds from ~20s to maybe 40 at best.

I've seen this same issue with no answer so far on this forum.  Should I just downgrade to the 600MBs service?  Maybe even back to the 300MB service with boost?  No point in paying more money for less bandwidth.