Is it obligatory to make up prayers in which there was hesitation and whispering (waswasa) regarding the pronunciation of the word "peace" (al-Salam) in the taslim, such that "al-Sa-" was pronounced, then the worshiper paused briefly before completing the taslim? And does this invalidate the prayer, or is it considered stuttering?

As long as you uttered the complete word of "Salam" (peace), your prayer is valid, and you are not required to repeat it. Your prayer is not invalidated by saying "As-sa..." before completing the full salutation, especially if you suffer from obsessive-compulsive disorder. A person afflicted with OCD is considered overwhelmed, and jurists have stated that one who is overwhelmed by speech during prayer does not invalidate their prayer.