He's in his fourth year. He's had different coordinators, coaches, and Manning himself try to work through his problems. Most people cannot throw a football well enough to be an SEC QB. Some folks unfortunately cannot handle the mental or emotional aspect of being an SEC QB.
One of the things I've noticed about JG is that I can't remember ever being tricked by a handoff. There is just no stealth or deception that I see with other quarterbacks that leave me following the wrong man. I think that could be a valuable skill.
JG has an issue with seeing the field. He cannot find open receivers and when he makes the right read he cannot get the ball to the WR half the time. He also has these WTF throws where you can watch it back and have no idea wtf the kid was thinking. I have no idea what has happened to him but something made him regress heavily since last year.