think our mileage was rolled back

[1989GT]

Not sure how to tell if the odometer has been rolled or not, but I will say this. I've never seen a ring and pinion need to be replaced from just driving. I have seen them give way in a racing environment. I curious to as why a dealership would but 27k miles on a car. I'd say your best bet would be to take it to a ford dealership and tell them what you suspect and have them look it over. Possible the car's just been driven really hard. Also what gear ratio was in the car? And what ratio did you have put in.
-Ryan