Rear and Front Axle Fluid?

[RoadKing]

I would like to put some AmsOil differential fluid in but manual does not say how much is required. The AmsOil is expensive so I only want to buy what I need. Truck has near 6k on it. Do not need to change it yet just want to get out the wear in fluid and put in fresh now.

Anyone know how many quarts the rear and front axle reqs?

Thanks.

Happy New Year!