The wire measures 53Ωs at the sender AND at the fuel gauge. But you are correct. there is nothing left but to reexamine the grounding.
I redid the grounding. I even made it single point grounding, what does not matter at all. I thought about ground loops but that is not applicable.
Everything I did and the gauge did not change.
When I was a microwave engineer, somewhat fresh out of school, we had a term to describe this It is "FM" (******* magic)