Fuel Sender Issues

[RPOLS3]

I am having this same issue in my Chevelle - installed new tank and sender last night to replace cursty but working original units. Tested new sender prior to install. Hooked up power wire to sender then hooked up ground, moved the float up and down and the gauge in the car worked as it should. Installed everything and put 5 gallons of gas in car and the gauge reads empty. If I disconnect the power lead to the sender the gauge reads full. I had to drill a new ground as the new sender wire was too short to make the old location work, thinking that might be the problem. Ran out of time and will try again this weekend......ugh.