So i was talking to one of my mechanic at work the other day about possibly buying an xterra. I explained to him that i was mainly concerned w/MPG and reliability. He mentioned that on many American trucks adding manual lockers can increase your MPG by about 10% or so. Anybody have a take on this? And if so whats the theory behind this? The auto hubs should be freewheeling all the time unless you don't go through the proper procedure to disengage them....So i don't see how having manual hubs in the unlocked position would make a difference. Thanks for any help