Problem w/ Fuel tank gauge sending unit 2009 Chevy Silverado, 26 gallon tank

Sorry but the audio is not very good - 2009 Chevy Silverado, 1500 extended cab 26 gallon tank the gas tank is empty when the gas gauge says half tank so I pulled the pump unit and replaced the sending unit. It's supposed to read 40 ohms full 250 ohms empty so I checked the sender itself and got 40 ohms/250 ohms but when I plug it in I get 40 ohms/180 ohms. I cannot figure out this problem. Maybe wire between sending unit and plug on top of the pump assembly is bad.