tachometer and charging meters don't work after sitting for a few days

You may have a defective crankshaft position sensor, wiring or Powertrain Control Module issue. On a Diesel engine, the PCM controls the tachometer and charging system. Unlike it's gas fueled counterparts, the diesel will run without these inputs. Also, without engine RPM information to the Transmission Control Module (TCM), the transmission cannot shift and will go into default mode, (2nd gear).