Misspeak to me means something different. If I mistakenly say that A is true when I know that A is untrue, and if that mistake is simply a mistake, that's a misspeaking. But if I say that A is true when I know that A is untrue and I am trying to hoodwink you, that's nothing more nor less than a lie.

But wordsearcher is looking for a word that describes a person who says wrongly that A is true and sincerely believes it, even though A is not true. IMHO misspeak doesn't do that.

TEd