97 Manual tranny

Is the P501 a code you received from your truck? If so, the P0501 code is the following...

DTC Code: P0501 Description: Vehicle Speed Sensor A Range/Performance Probable Causes:

1. Sensor or solenoid faulty
2. Connector terminal contact is damaged or corroded
3. Wire harness - Check harness for correct voltage, open, short to ground or short to voltage
4. Update control unit software - Check for the latest control unit update
5. Powertrain or Engine Control Module faulty

Otherwise we would need a little more info on what the actual trouble is. If filling the reservoir helps and then it was bad again I would think you are losing fluid or that there is air in the system. There are two cylinders to be concerned with on your truck and they are the clutch master cylinder where you filled it and then there is the clutch slave cylinder located within the bell housing. Either of those or the line between could be leaking fluid.