Has anyone had ear fullness for years despite mouth guards for tmj?

Never seen that. A symptom of tmd can sometimes involve the ear usually manifesting itself with soreness at the anterior wall of the outer ear. Ear symptoms range from soreness, ringing, or deafness. Best to see and ear doctor first before seeing a dentist (ent).
Yes. The temporomandibular joint, or tmj, is immediately adjacent to and intimately associated with the ear. So, yes, ear fullness may be due to temporomandibular disorders (tmd). However, there are also other things that can cause ear symptoms. Only a doctor can tell the difference between a true ear problem and a TMJ problem. A mouthguard may not be the answer, and may cause more harm than good.
Possible but. Have your ears have been checked and tested? That is important. Also, tmj/tmd can be maintained and not really cured, but you may need more therapy than just a mouth guard. The mouth guard may also be a terrible mouthpiece for your tmj/tmd. I would see a specialist...You need a different type of mouthpiece, therapy and home exercises.