this video delves part way into the rear axles and ratings for the F-150 HD 9.75" and light duty Super 8.8" rear axles while showing part numbers.

It seems I've left some info out like how the different twist forces between light, medium, and heavy duty axle shafts and how they can change the shift feel of the truck and transmission when empty. making the light duty axle feel smooth because of the allowed deflection, while the HD axle truck can shift hard when empty because the truck is too light to allow axle twist (which absorbs drive line shock) so it feels rigid. If you put a ton in the bed or a trailer behind, the shifts seem to smoothen out because the "springy" effect of the twisting force on the axle shafts allows it to soften the blow.

This is the real benefit of the 8.8" light duty axle is it shifts smoother and produces less NVH along with better fuel economy for when lightly loaded.

The 9.75" when empty can be so abrupt or harsh some people may think there is something wrong with the truck or transmission. It will soothe out with a medium to heavy payload.