Fuel gauge issues

[lestraveller]

Can anyone advise me please. I've been trying to problem solve. I've looked through the threads and didn't see the answer I wanted.
Problem: my fuel gauge skips from 1/4 to full. When I fill up. After a while of driving it reduces from full to 1/4. Missing the middle bit.
I've took out the sender and tested it with my 12v light thingy and as I raise or lower the sender it lights up brightens and down as it should. Showing no light jumps. So my sender is working fine.
My fuel gauge acknowledges the re fuel but jumps down to a 1/4 after a long drive.
Can anyone confirm the problem is my fuel gauge in my speedometer.
Spent many hours trying to solve this and really need some advise.
Les