So my rear differential broke nothing else was wrong. I got a used one at the junk yard and my mechanic installed it. Runs great except it is in 4 wheel drive all the time now. I push the button for 4 hi and i used to feel it shift now nothing I can switch into low and back into hi and then auto. But when I start it again its still in 4 wheel drive isn't auto supposed to disengage and go back to 2 wheel when you start it? Any ideas on why it isnt?