Some good material to follow, beyond the publicly accessible history of the project (which is long, since the fact that M113 was deficient was known before the final direction of the replacement was figured out), using somewhat popular formats:

https://old.reddit.com/r/WarCollege/comments/erpmjm/having_j...

https://www.secretprojects.co.uk/threads/truth-to-the-pentag...

And finally a bit on the background of the Fighter Mafia member who wrote the black PR book that was used as basis for the movie (PhD thesis on the Fighter Mafia/Reformers and their influence in decision making in both USAF and elsewhere):

https://krex.k-state.edu/dspace/bitstream/handle/2097/38768/...