Well, while it is certainly true that Part I served as more drama for FFC, the most 'drama' set of the three was apparently the third one. I think it had everything to do with the fact that everyone had an ego and had become so much bigger than they ever could have imagined. It was reported if i remember correctly in Vanity Fair's article "Under the Gun", that discussed the various fights and arguments that broke out on the set of GFIII. They included, if i remember correctly: the obvious Robert Duvall dropping out, Pacino asking for more money and FFC threating to rewrite/shoot the entire movie to begin with his funeral, Talia Shire and Diane Keaton's battle over top billing. Of course the biggest focus of the drama was the casting of Sofia as Mary which resulted in, once again not sure if i remember correctly, Pacino and Shire threatening to quit the movie. Also, Franc D'Ambrosio was treated poorly on the set by other castmates, crew, etc.