I have the 3.73 with electronic locker. Ever since i've run it in tow mode ive increased my mpg average from 13mpgs to 15mpgs driving the same places. It seems to me the 6th gear is more for if your on open road all the time where i live it just makes the truck a pain and trys to shift to frequently going up hills or anything causing the truck to fall on its face and then dropping a few more gears to pick itself back up. In tow mode it doesnt do this, i can see 6th gear if i was to travel the highway but i never do thats why I also got the 3.73 gears. Also alot of the grades I travel are between 5 to 10% all the time its very hilly around here if your not going up your going down.