the gears are coated with a phosphorous coating to facilitate break in so its critical to change the break in oil at 500 miles, if I remember correctly or trucks require synthetic oil for the diffs.
I typically use Amsoil in all my stuff

Neal

 

Update:

Received the truck Friday afternoon. Everything was in great condition, I'll bring it back at 500 miles for an inspection and fresh oil.

 

Wouldn't worry too much about it. If its good in that 500 miles, you'll likely never have an issue. Rest of the drivetrain will be fine being drug a little too. Just keep an eye for any leaks. Usually these diffs leak out of the outer axle seals until they weld themselves together because no one notices.

 

Remember the front diff is a little fussy as far as fluid, Put in to much and you will find diff oil slinging out of the axle seals. Some like to fill them way past the level of the plug, not a good idea,