Plot hole: When Forrest finds out he is receiving the Medal of Honor, he is addressed as PFC Gump (Private First Class, E3). "Two weeks later", he leaves Vietnam, and is then shown receiving the medal from President Johnson. In this scene, he is wearing Sergeant's stripes (E5). There is no indication or mention of him receiving a promotion, let alone two. (01:02:10 - 01:03:05)
Forrest Gump (1994)
1 plot hole - chronological order
Directed by: Robert Zemeckis
Starring: Tom Hanks, Sally Field, Gary Sinise, Robin Wright, Robin Wright Penn
Factual error: During the 1972 New Year's Eve celebration, Forrest drinks a Dr. Pepper with a logo that wasn't devised until around the mid 80s.
Drill Sergeant: Why did you put that gun together so fast, Private?
Forrest Gump: Because you told me to, Drill Sergeant!
Trivia: Dave Chappelle was originally offered the role of Bubba in Forrest Gump in a pre-production stage. He was concerned that the character was racially demeaning, so he turned down the part. He has since admitted to regretting the decision.
Question: What does Jenny die of? And is it mentioned anywhere in the film at all?
Answer: In 1981, when Forrest meets Jenny again, she says she has a virus that doctors don't know. This virus was the HIV virus, as 1981 marks the AIDS outbreak in the World.
Answer: It could have been HIV or Hepatitis C or something else. Maybe someone related to the story or even Winston Groom himself told this at some other place. Nonetheless, it's false that it appears in that book.
It absolutely appears in the second book, 'Gump and Company'.
Answer: It's not specified in the film, but in the sequel book "Gump & Co" the author mentions that Jenny dies from Hepatitis C as a former drug addict in the early 70s. Hepatitis C was an unknown disease until 1989.