If the sending unit is going from 0-30 ohms, then I would say the sending unit is good. The next place to look would be the ground wire from the sending unit to the where it goes. Many times the frame. You can do a voltage drop test by putting a large light bulb like a headlight bulb on the ground wire which goes to the frame. Check the voltage on both sides of the light bulb as it is glowing with the meter lead on a GOOD GROUND. On one side of the bulb you should have battery voltage. On the other side you should have less than .25 volts, but preferably zero. If you have more than about .25 volts, you have a bad ground.