Unable to find Franklin's last mission

I've passed Mission #65 'Legal Trouble', but that's as far as I can go.
Franklin has one mission which is nowhere to be found. I took multiple cab rides, I called Tonya but she's busy, even though I've finished her missions as well. I can still switch between all people. When I call Trevor or Michael, they just say we have business to handle. All the night-races and parachuting are done as well.

Solution 1:

Once you finish Legal Trouble with Michael, a mission called Meltdown should be unlocked for him ONLY if Lamar Down has been completed.

This might be the mission that you are missing from Franklin to continue the history. You can start it from his mansion at 3671 Whispymound Drive.