Okay, so this achievement originally didn't unlock for me either. When I completed the game the first time, I had every achievement except for the speed run and Movie Mogul. I had done, I'm certain, everything required and was quite disappointed when Movie Mogul didn't unlock.
However, I knew I had to do another play through to get the speed run achievement, so I wasn't giving up hope yet. My first hope was that it would unlock as soon as I finished the speed run, because on the PS3 Movie Mogul is the platinum trophy, meaning it unlocks when you get every other trophy.
So, I did my play through, and actually set my final save right after I defeated Kip, but BEFORE I went to talk to my Uncle in the penthouse to finish the game. So, then I talked to my Uncle, got the Speed achievement, and nothing....no Movie Mogul. Well, that was my first hope shot down.
So, then I went about collecting the trophies, completing the seductions, and finishing the races. After I finished all 9 races, 7 seductions and NINETY-NINE trophies, I re-ran another race to create a new auto-save, then went to my trailer to create a manual save. Then, just to be safe, I quit to dashboard and made a copy of the auto-save and that last manual save. I wanted to have the ability to try grabbing the final trophy before OR after I talked to my Uncle to complete the game.
Now, I went up to the penthouse, and talked to my Uncle, to complete the final story mission.....no achievement. Then I ran to the final trophy, climbed up onto they Bytanic lot propane gas tank, grabbed the final trophy, and.....nothing. But just as I was about ready to cry.....PLOCK! (how do you spell that sound?) Movie Mogul unlocked. It probably took about 15 seconds after I collected the final trophy.
I really sympathize with those who haven't been able to unlock this. The game really wouldn't have been too bad if it wasn't for the horrendous controls and camera (I guess that means gameplay in general, lol).
Good luck to those trying for this in the future!