Fuel Sender / Gas Gauge

[P2mac]

I am trying to figure out which of the above I need to replace on my '98 1900SR. The gas gauge will not go below 1/2 tank. I disconnected the pink wire from the sender and the gauge dropped to empty. I pulled the sender from the tank. When I move the sender arm, the gauge moves. However, when the sender arm is dropped all the way down to vertical, the gauge only drops to 1/2 tank, not empty. Do I need to replace just the sender, or do I need to replace the sender and gauge? I cannot find anywhere on the sender or gauge where I can do any kind of calibration.

[mmwjr]

To test the gauge you remove the sender wire as you have and it should read empty then ground the sender wire and the gauge should read full. If both pass the sender is bad.