Thanks for the information. Some of us from the rear wheel drive days think of a differential as a rear differential. You have no separate rear differential on a Taurus. The rear differential takes "differential fluid or gear oil". However there is by definition a differential which is an integral part of the transaxle, still able to learn. So your two months ago ATF
+ filter service pan drop changed the fluid for the transaxle as well as the integral differential. So the answer to your origninal question is yes, you do need to change the differential fluid. As Roach stated " change the tranny oil, changes the "differential oil". You are set. Have it done or change it about 30,000 miles from now for optimum trans life.