Albert Barnes Commentary Exodus 4:10

"And Moses said unto Jehovah, Oh, Lord, I am not eloquent, neither heretofore, nor since thou hast spoken unto thy servant; for I am slow of speech, and of a slow tongue." — Exodus 4:10 (ASV)

Eloquent - See the margin. The double expression slow of speech (Ezekiel 3:5, margin) and of a slow tongue seems to imply a difficulty both in finding words and in giving them utterance, a very natural result of so long a period of a shepherd’s life, passed in a foreign land.

Since thou hast spoken - This expression seems to imply that some short time had intervened between this address and the first communication of the divine purpose to Moses.