Which rear differential oil is currently recommended for 9.75 inch standard diff on 2001 Ford Expedition

originally, Ford recommended 75W-140 synthetic. My Ford Master Tech. Friend says it is better to use 80W-90 regular diff. Oil because 75W-140 gets too thin in use. Have you heard of this? Which do you recommend?

Asked by for the 2001 Ford Expedition
The safe bet is to go with the factory reccomended fluid.