Is Mobil 1 75w90 good to use in my front and rear diffs?

yes

Honestly, just drive to your local auto parts store and pick them up in person. I don’t get why people order stuff like gear oil on Amazon.

fortuna said:
Honestly, just drive to your local auto parts store and pick them up in person. I don’t get why people order stuff like gear oil on Amazon.

Only reason is the price — I can get 6 quarts online for way less. Local stores charge nearly $100 for the same thing.