What truth is revealed about Jim?
I think that one of the basic truths revealed about Jim is that he believes in Changez. Jim believes in both the worker that Changez has become, but also in the person he is. Jim can relate to Changez because like himself, Changez is an "outsider." Jim also believes that there is a certain amount of solidarity between he and Changez:
In wartime soldiers won’t really fight for their flags, Changez. They fight for their friends, their buddies. Their team. Well, right now your team is asking you to stay.
When confronted with the prospect of Changez leaving, Jim offers these words as a form of encouragement. This reveals his belief in Changez and how he identifies with him. Such a notion is also evident in how Changez's narration does not show Jim to be angry or vengeful at the decision that Changez made. The end truth about Jim is that he does represent the promises and possibilities of America in a time where so much of these are blighted by its pursuit of foreign policy at the expense of nations like Afghanistan and Pakistan. Changez's railings against America fail to incorporate the character of its people, as represented by characters like Jim.