Fuel level gauge problems

Recently, I swapped my leaky factory plastic 20gl. tank for a steel 15gl. tank. Some of the hardware was different, but it went in O.K.. Before the swap, the gauge would read 1/4 when the tank was empty but it would always work. After the swap, with a new sender, the gauge would read accurately but it would not work all the time. I figured the gauge was bad, so I purchased and installed a fuel level and temp. gauge from Autometer. I installed both gauges as per Autometer instruc. using new wires for all connections and soldering each connection. The battery was also disconneced the whole time. After the install, everything except the fuel gauge worked properly. The needle would move from the pin to the "E" but no further. The same thing as the old gauge. I double checked each connection and made sure there was clean metal for every ground. I am reading 23.8 ohms at the gauge with about six gallons of gas in the tank (on a scale of 73 to 10 from empty to full), and 12.5V at the "hot" post on the gauge. All the readings and connections seem right to me, but the gauge doesn't move past "E". I even added gas after the first check to make sure there would be enough to register ( from 2 to 6 gl.)
Is there any way to check the gauge before I send it back? What could this be if not a bad gauge? If there is a bad ground on the sender I wouldn't get any voltage, right?

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