If there is no record of a transmission fluid & filter change, I would recommend doing that as well. That way all of them will have the same mileage. Change intervals are similar for all of them as well. That one takes 8 qt / 2 gallons. I bought a filter from RockAuto that was a perfect match, but the included gasket was for something else. I used this to seal the pan. Follow the instructions carefully, don't overdo it.

 

Transmision fluid needs to be changed more often then differential fluids. Differential fluids are not usually exposed to engine and exhaust operating temperature and the obvious about 10x+ more parts that can be affected by not more routinely changing the fluids. The one big argument for more deferential fluid changes is that most are not oil pump and pressure lubricated so they tend to bult up sludge that settles to the button of the case more than in a automatic transmission.