I was watching a game play video online earlier today and noticed the guy playing had the option to replay 75 story missions, 3 more missions compared to my 72 after completing story mode.
I did reject a mission to help Michaels son towards the end of the campaign but otherwise i am certain i accepted all available missions.
Any idea where i would have missed these 3 missions? I have yet to replay the alternate endings (i picked C) but they are now in my list of available missions. I also replayed the jewelry store heist and was not required to do the mission to obtain the rifles.