Agree with Avalon on the info there.
Are you making sure you have a clean connection between your Fire Stick and the WiFi connection to make sure that isn't part of whats causing the buffering? The net connection not being congested at home from many devices using it? And of course the channel isn't overly crowded?
If all of that is yes, you've checked, then I would then ask if you have Dev Unlocked your Fire Stick and installed any... er... "Modifications" to it? As reduced storage space as well as unfriendly background applications, can cause the Fire Stick to slow down something like Iplayer or Netflix.
If all of that is no as well, then I would suggest going into the settings and disabling the suggestions and auto-retrieval stuff that it pulls from the rainforest that is default set to "On", as that can chew up process' too on the Fire Stick.
Hopefully something in this list would help you find out where a possible issue is so you don't need to do something drastic and unnecessary to get things working smoothly.
(Quick Reference: I have a HH4 (Dual Band Capable), that was previously on 2.4ghz only, but I've disabled the 2.4ghz and left 5ghz on only recently after updating stuff. It only services the Fire Stick and an Ipad within a 2m radius, and the Fire Stick within 30cm. All with clear line of sight, and other than when it loses the connection to the net via the main router in the house, it has never had any buffering issues before on any of the devices even on . Main net at 72 down/20 up. So again, I would take a gander to see if there's something that you can fix there without needing to do anything funky or unnecessarily expensive to solve the problem.)