I have my deceased husband’s 98 Ford F150 pickup. The last time I had the oil changed the service manager said next time we would “do the differential.” What service is required on a truck differential?
There is a fluid change at some point. Check the interval in your service schedule.
I have a F-150 1994 I change it about every 25,000 miles, I sure that is the specification in the book.
Follow the advice of your service person, it will cost you less money down the road.
If the truck has been through any deep water get the differential fluid changed out right away.