Gas guage only registers 1/4 full

[8door]

Here we go again.
Got a new tank sender, checked the power connection, made sure
tank is grounded as well as the base of sender where it sits on tank.
I know tank is FULL of fuel but ithe guage only registers 1/4 full.
Took the sender out again made sure power and grounds firmly connected turn on the switch slowly moved arm to maximum sure enough guage stopped at 1/4 full.As I slowly moved arm back down the guage started to move toward empty.
Then disconnected ground and guage moved all the way to full.
What am I missing ??????