I recently replaced my factory auto lockers for a set of MileMarker manual hubs. Interestingly enough, I noted a marked improvement in gas mileage. Since my gas mileage hasn't changed since the day I bought my X brand new almost 2 years ago, this tells me that my autolockers haven't worked correctly since the day I took delivery of my truck. I found this rather interesting and was wondering if anyone who has done this experienced the same thing or is it a fluke? I have seen close to a 2 mpg increase in gas mileage since the install. This leads me to believe the hubs were not fully disengaging when they were supposed to.