I know a well known and accomplished drag racer that ruined a set of fairly new 4:86 gears in his 1971 Dodge Demon 8 3/4 in one run trying either 30 or50 Wt. racing oil in the rear end for one run
I use ATF in my NP833 18 spline pro shifted drag racing 4 speed for 2 1/2 years in my old 1970 Hemi Cuda, worked good, lasted a long time
I would change it about every 40 runs after doing maintenance on the gears and sliders