What is the author's style in Forrest Gump by Winston Groom?

Author, Winston Groom, writes Forrest Gump entirely in the narrator's Alabama accent. He opens his story about a life that is "no box of chocolates," but "pretty interestin" nonetheless, by stating that the main character's IQ is 70, which is borderline imbecile/moron, but he prefers the term "halfwit." Forrest immediately tells an anecdote that shows he knows when he is being cheated and that he should react more "normally," but instead he walks away, feeling all the more like an idiot. Throughout the novel he demonstrates his ability to see reality and accept everything that comes his way as inevitable. He narrates with a flattened emotionality that is broken only by the most wrenching events—the death of his friend Bubba and the loss of his girlfriend Jenny. Both narrative portions and dialog are filtered into his dialect, so characters have no distinctive voice.