An auxiliary electric fan will help, especially for a/c performance at idle. Enough so that Ford builds an ambulance prep package with the “gulf coast upgrade” kit which is exactly that. An electric replacement fan however won’t move as much air as the mechanical fan, so it’s not recommended for v8 and v10 motors.
But before doing that.... is your fun clutch working? A/c system at specified pressure? No debris plugging the evaporator?
2000 E450 dually V10 wagon