He is over 3 years old.. so typically the free early childhood prevention services would not apply.
But yes, for enunciation issues.. it is best to see a Speech Therapist... because they have the professional knowledge about how to work with that... and they do an overall assessment, to pinpoint any problem areas that need work on.
My son had speech therapy before 3 years old. He was just a late talker. BUT.. .it gave us enormous knowledge, about speech and how it develops, PER the age of the child... and the mouth coordination development, hence enunciation... and at what age certain sounds are or are not yet developed, yet.
Speech and enunciation... is age based development. Or sometimes there are mouth coordination issues, which a speech therapist can address.
Keep in mind, that talking/speech ability has NOTHING to do with "intelligence." Einstein did not talk until 3 years old and I believe Mozart. And they were geniuses.
My son was late talking... for his age. But, he was assessed, overall, and was found to be even Advanced in development, in several areas. He is also very bright for his age and bi-lingual. But, his late talking was not a reflection of his "intelligence" nor abilities.
Through speech therapy, I as a Mom, have learned many things and technical things, on helping my son. But yes, even when he was not yet fully talking, even other Moms would talk "down" to my son, thinking he was stupid and asking me point blank "what is wrong with him, how come he doesn't talk like a big boy...." Rude. Very rude. My son, of course is not deaf, and HE can hear those comments too.
Seek out at least getting him assessed. Why not? It is only to help your son and/or determine IF he needs help, or if his enunciation is "normal" or not, per his age.
All the best,
Susan