I will recap what I have done and what I am doing next;
I started with a firestick and VPN with a 100 Mbps plan and wireless router and using Dexter IPTV.
Tried with the VPN on and off no difference. Download speed between 70-100 Mbps with the vpn off, and 30-40 Mbps with VPN on.
Switched IPTV service to instaplay did not help but the quality looked better.
That provider suggested I loose the firestick for a BuzzTV XRS 4500 so I did. it did not help.
Upgraded my Comcast from 100 Mbps to the 200 Mbps plan. now Im getting 150-180 with VPN off and still 40 on. No change still lots of buffering.
Did a trial for a new VPN it did not help either speed or buffering.
Was suggested I wire the modem straight to the BuzzTV box, did not help much.
Instaplay said only I was having problems and even sent me a video of the same channel playing with no buffering.
It was suggested here on STB to try a different server and I did use the one recommended with no improvement. lots of buffering on a few channels.
My next steps starting tomorrow.
A new modem and new wireless repeater.
if it still does it then the only thing I have not changed is Comcast other than to upgrade the speed.
I dont know if they have found a way to throttle me without dropping my speed test scores (and getting past my PVN with scramble turned on)
If I had to guess I would say its my internet or modem. some of my speed tests give great scores but are not smooth. that could be a modem thing or Comcast I guess.