Question about the final Lester assassination mission (The Construction Assassination)?

I just recently did a second playthrough of GTA: V, and this time around, I decided to try utilizing the stock market via Lester's assassinations. When I got to the last assassination, I invested all of my money, on all 3 characters after, in GoldCoast on the LCN BEFORE the mission, which is what all the websites (IGN and others) say to do, and then did the assassination. Websites like IGN and others say you should be able to get a 75%-80% return, and that the LCN stocks usually reach their peak about a day or so after the mission. I've tried this up to three times, but it only goes up to 35%-40%, and then starts to fluctuate. Even tried sleeping through almost a week in-game time. Am I missing something?