Fuel Gauge Needle Viabrating

I have a 99 Express 1500 4.3L automatic. I recently replaced the generator and ECM. The fuel gauge is working, but the needle is viabrating. I have never seen this before. It does this even with the engine stopped and the ignition switched on. Does the dash have its own voltage regulator?

You are prob wondering why 24 people had nothing to say....me too. I have the same problem on my 99 2500 4.3. Pump hasnt went out yet, keep your fingers crossed!

The vendor that supplied the replacement ECM said to fill the tank half full then disconnect the battery for 4 hours. We'll see.