Hey Sprint
I researched the hell out of this (ENTs weren't helpful) and I found something called Tonic Tensor Tympani Syndrome. I'll let you go ahead and research it on your own, but this condition describes my situation almost exactly with respect to that "fullness" feeling. The fullness feeling can be the result of many things, but usually for people with some sort of hearing issue it is due to this. For me it's more of a tightness sensation and a "tugging" sensation on my ear drum.
Strangely enough, if I put plugs in or my IEMs it basically goes away. Sometimes when it flares up I get pain under my chin, near my eye and down my neck. Almost like a burning sensation. Other times it feels like there's water trapped in my ear, but doctors found no fluid or wax. You may just be experiencing Eustachian Tube Dysfunction, however that's not what I am experiencing. Does any of this match up with what you have?
Interestingly enough, I don't have tinnitus - at least nothing I can hear or notice. I'm trying to avoid it if I can. I've learned a lot about ears over the past couple of months and it really is amazing the pounding that we give them. I know there was a poster on here who was a very knowledgeable audiologist, but I can't remember his name. He may know more.