well i got 170,000 miles on never been changed ever fluid in a 95 sonoma and as mjr46 said a lot of manuals dont even specify to change it, so i was wrong as usual but i never had any problems never changing it

 

I've had 2 S10s that I will promise had over 150k on the original diff fluid.. BUT.. There's a big difference between my 2.2L open carrier S-10 rear that really can't be abused (they put essentially the same rear in LS1 cars), and my Mustang's LSD 8.8 that gets beat on.

So, back to point 1, the Mustang gets changed every year (3k miles for me). Fluid is cheap.