mcgreggr It has to be either not enough protein extraction (doesnt sound like it from your 8 minutes back and forward) or smoke schedule. So, I think you are probably going too hot too quick. What is happening is the fat is rendering out of the meat and being pushed out, it then gets trapped just like you are saying.
Also, beef fat tends to have a yellowish tint to it so I’d recommend pork, that has a nice white color to it and it is creamier.
THe other thing I would do is to add a binder like sure gel!