what are the pros and cons of using the auto 4x4 on a 97 expy with the 5.4? not the 4hi, or 4 lo,, but the automatic full time 4x4,,,, will it affect mpg? will it be safer, like in the rain? will it wear out certain parts quicker? when can i tell it kicks in? would it cause tire wear issues? especially at high speeds like 80? does it even kick in that high? i know different tires pressures make it kick on from reading old posts on here (great site and great people that really help) how exact do they have to be for the little reader thing to know when to kick in the 4x4?