Was Moses a Stutterer?

Those last two phrases—heavy of mouth and heavy of tongue—are a literal translation of the Hebrew. Most commentators have taken them to refer to stuttering. But some of the rabbis, who wrote about this story for centuries in the Mishna and Talmud, didn’t think so. The eleventh-century rabbi Abraham Ibn Izra thought Moses had a speech impediment, but not stuttering. The rabbi wrote that Moses could not produce all the normal sounds with his tongue and lips.

http://www.firstthings.com/onthesquare/2013/09/was-moses-a-stutterer