In the original ending, Rambo and Troutman talk in the gun store that he is holed up in, and both come to realize that Rambo will never be able to live a normal life, and so Rambo asks Troutman to kill him, since he would rather die at the hands of a soldier that he respects, then Troutman shoots him. It is such a gut-punch after routing for him the whole movie, but the more you think about it, the more sense it makes that that is the only sensible way to end it. Plus since it was really meant to be an anti-war movie, the original ending fits that theme much better.