1996 Chevrolet Suburban "change front differential fluid 96" Questions

it would get stuck in 4wd low and enter 4wd low on its own. I fixed this by changing the front differential fluid. I believe it was low and being low didn't allow the 4wd actuator to function properly

front axle should take SAE 75W-90 oil and the rear takes as follows: Ambient temperature usually above 50°F (10°C)-SAE 140W Ambient temperature usually below 50°F (10&