I think I know where you are coming from; I did/do the same thing, have the same "need" to be understood. I was in therapy for a long time to help with that, don't know what I would suggest to you other than maybe the more you are "aware" you are feeling that way and just do as TheByzantine says and "stop"/stifle yourself maybe the need will lessen?

I guess I would first try to learn to preface my explanations with a "joyous" look lit-up eyes and big smile of gratitude and then a kind of exaggerated, "Oh! I thought. . ." as if I'm really glad it was clarified. They might not see that as arguing, might just think I'm "slow" to understand.

Of course, one might not want one's boss to think one was slow so I'd train myself to first respond to something with a "code" word or expression to myself that would help me learn to not explain beyond a particular point, except in my head. I'd maybe immediately say, "Oh, I get it now!" or something innocuous like that.

Maybe if you treated explaining as if it were "punishment" and made a note of it and wrote it out in a journal at night after you got home or something? Or, if you do a desk job w/computer to yourself, maybe type it up in a personal file quickly instead of saying it?