In the Book
In the Movie
Forrest is a huge man. He is 6'5" and 242 pounds.
He is average size.
As a child Forrest's legs are perfectly healthy.
He has a crooked spine and requires leg braces.
Forrest becomes and astronaut and goes to outer space. He meets an ape there named Sue. They crash in the jungle and are taken hostage by cannibals.
This doesn't happen.
Forrest becomes a world class chess player.
He never plays chess.
Forrest and his Ape grow shrimp in shallow pools.
He has a shrimp boat and catches the shrimp in the open water. Lt. Dan works with him.