Alright, Ive searched and can not find an answer so I thought I would ask. When I put the truck in 4wheel drive the hubs lock in but when I put it back in 2wheel drive they do not unlock. I have tested the hubs and lines and they all hold a vacum. I read some were that it takes -15psi to engage and -30 to disengage??? Is that right?? P.S. Took a new set to see if it was the Auto hubs and it still did the same thing.