In the center of the State of Florida, most will find that the dialect is very southern, and can be hard to understand if your own dialect is of the northern variety. When I moved to the Tampa area more than thirty years ago, people thought I was from Louisiana, or from somewhere in the Deep South.
After the debacle at the base of Mt. Sinai, with the golden calf worship, it seems that Moses began speaking to the Israelites himself, rather than through Aaron. It makes me wonder if after meeting with God on the mountain, Moses got over his fear of speaking, and no longer worried what the Israelites thought. Did Moses truly have a speech problem, or was it merely a dialect difference? He was brought up by the Egyptians, so he may have still been learning the language of Israel.
When God has a job for you, he equips you with the ability to carry it out. If you feel inadequate, just go slowly until you get some momentum, but if the Holy Spirit comes on you with all power, nothing will stop you! When fear sets in, remember Moses; also remember Peter who preached to over 3000, and was just a country boy who liked to fish.
Afterward all the people of Israel came near, and he commanded them all that the LORD had spoken with him in Mount Sinai. Exodus 34:32