I had(have) the same problem with my then 318 powered Challenger.
I used to autocross a few times a year with the car, it was common to lose the fan belt during a run.
Someone suggested removing the fan and fan clutch before a run.
It worked, belt stayed on! If you're still running a stock style clutch and metal fan I'd try a run with fan removed.
I'd drive to the event and remove the fan, wasn't too hard to do, and replace for the ride home.
I don't know if there's a lighter fan and clutch I can try. Or if the fix is going to be adding an electric fan.