when are you having it happen (out wheeling, driving to the store, etc)? can you recreate it on demand? I'd like to know a little more about when it happens to try to ID the cause.
did you build the duals or buy the truck built? I'm not too sure what you mean by 'I then unbolt the shift rod on the rear case and can manually shift the transfer case'. Do you mean you remove the shifter base? the only shift rods are internal and held in place with roll pins.