The early model 04-07 diff failures were supposedly attributed to a poorly sourced ring or spider gear which was sorted out in the 08' models. I own a 12' Pro4x with the GKN electronic locker and from my knowledge there are no reported failures of the GKN electronic locking rears. I added a replacement mag-hytec diff cover then closely monitored wear-in of both front/rear diffs and transfer case which broke in beautifully with minimal wear. My mileage hovers around 13mpg with GoodYear Duratrac 275/70-18's and a slight front lift with the Bilsteins. Power is outstanding, mileage not so great. I've been very happy with this truck having owned Ford, GM and Toyota. Sticker was $42k on mine and I picked it up for $34k so I felt like I got a fantastic deal at the time.
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