What kind of gear oil for 8 3/4? Why not synthetic gear oil?

I use Mopar synthetic 75W-90 in my 8.75 race car. Mostly because I get it for free. If I had to buy it I'd probably use Amsoil of similar viscosity.

The race car is equipped with a pro gear and a spool so no limited slip to worry about.

The tow vehicles have always had 75W-140 Mopar synthetic in them.