Does your speedo work? Sometimes unplugging and checking out the two wire connector on the trans or transfer case has a bad connection. THe speedo is part of the OD shift, and also the trans temp sending unit on the front trans line coming out of the trans. Could be a worn out TPS unit that sits on the top of the injector pump. All the auto trucks I've had, have had to replace them sooner or later. But kinda weird that it happened in a middle of a trip!