Gas Gauge/ Gas tank question for a ' 91 Plymouth Sundance

Hello, I recently replaced my gas tank in my Sundance, it was getting very rusty around the sending unit area and was starting to leak. Everything is back together and it is running well with no leaks. The new problem that it has, when the car is running, the gas gauge shows less than empty, even though it has a considerable amount of gas in it. When I shut the car off, the gas gauge slowly moves up to where it normally would be when it would be running. Did I somehow mess up the ground or did I cross something? This is my daily beater car and need a working gauge. Any ideas? Thanks in advance.

I sounds like it was incorrectly reinstalled or wired backwards. A good mechanic can quickly determine what’s wrong and advise you. There should be enough wrecks of this model to cannibalize a used one, if necessary.