I appreciate the response and without any disrespect, my experience with lockers or posi's or with the truetrac, I have noticed better fuel economy with these. The re-gear might have helped as well but I had a 71 k5 blazer with a 350 and automatic transmission. I averaged 19mpg on highway and after the locker installed on the rear, I increased the mileage to 25mpg on the hwy. So, with my experience they have helped. As for the speedo error I have that all recalibrated and is dead on. I haven't left anything undone on my Blazer. I don't hot rod around and abuse the Blazer. I also have 176k on her and try to take care of her best I can. Some people may get lousy fuel mileage because they are in the fun factor more often than not. Again, with my experience, they have helped with fuel mileage. Hard to understand but is true. Oh, by the way, My k5 had 31's and 3:73 gears, speedo was also dead on, it was also a stock 350 with a Edelbrock carb. If you look at my Blazer and attention to detail, does it look like I just blow smoke out my exhaust. I think things through and make sure everything works as needed, as one unit and as it should, not just throwing parts in just because I can.