John:
Check out the poppet valve on the transmission cover. This valve is apparently not sealing right to properly shift your transfer. You will find deep grooves in the face material, which, when too deep, interferes with the sealing of the poppet. I have taken them apart, carefully removed the old sealing surface material, and two-part epoxy bonded new sealing surfaces on the poppets. I still have some of the tough belting material I used if you need some. It has worked fine in the truck now for over five years. I was determined not to pay the very high price for a new poppet valve when I can use ingenuity to fix it.
When you park the truck and shut down, air pressure still in the system continues to hold pressure on the poppet, causing the face material to keep taking a set and depressing. Of course most of us leave the transmission in neutral or a forward gear when shut down, which keeps pressure on the forward shift poppet. I make it a habit to put the gear shift in reverse to put pressure on the reverse poppet so it takes the load off the forward poppet, evening out the wear. For this reason, you will see one poppet with little depression and one with a deep depression. Ideally they should have a flat surface of an elastomer that will seal them.
Regards Marti
