the overdrive does not work

Hi, I have a 2000 F350 XL: I found out Ford O.E,M, on my truck was a case hardened ring and pinion. I had a Off site Mechanic at a trany shop tell me this and that the case harden is only .003/.006 deep. Once you chew thru that layer you start to float metal on the oil in your housings and it coats the magnetic speed sensor. And it interfer's with the signal for O.D. shifting. Time for a new set of gears! Go full synthetics on your fluids!! I got 240K miles on my rear set before it started to go. And I was told that was exceptional mileage...they typically go after 150K with conventional 90W. Go full 4340 billet hardend steel and you can forget ever touching the rear ends again! Check around for a tech school and see if they do cars and trucks. deep discounts for learning projects.