After my first surgery in 1987 when I lost about 1/4 of my tongue I was lucky to regain my normal speech again. Since I taught college and later worked as a business consultant I did a lot of talking. I often described having "tired tongue" very similar to what you describe. It did improve with time but there was always some fatigue after long periods of talking. In 2001 I had more of the tongue removed and have more difficulty alhtough as Packer notes, at least I can still talk. My speech is more slurred and sometimes the effort to talk is more than I want to deal with. For the most part its still hard to get me shut up.