My dad has a 2002 Silvarado 4x4 and the front diff wont engage. He repalced the piece in the front diff that engages it but the buttons on dash continue flashing if you push 4hi or 4lo. niether he or I are that familiar with the 4wd system. The trasfer case sounds like it is engaging and the truck feels like it is in 4wd but the front diff never engages. Ca anybody help us out? Thanks.