I used the amsoil severe gear in whatever is the 75-90 weight, and tow a travel trailer. The fluid which came out at 30k looked good and i saw no cause for alarm. Mine was weirdly low by my old school thinking, and I also filled it to the base of the fill hole. It’s been fine. I don’t see the extra half inch causing anything weird, such as more cavitation than is already there. 2018 f150. For what most of us do, unless there is a design issue with the diff, IMO I don’t see the need for a 140 weight.
i did the tcase also. Now, Ford calls for their ULV formula in the tcase. Amsoil calls for their LV equivalent, which is a tad thicker. I went with amsoil. The drain magnet was very clean, but I don’t 4x4 much.