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Sounds like a fuel sender problem
This is located the the in tank fuel pump.
You would have to drain tank
remove the pump from the under side of tank and replace sender.
I would warn you there is no easy way to drain the fuel. Last one i did i loosend the pump so the fuel came out slowly into a large bucket.
Really messing arounrd with fuel if you do not know what you are doing is not a good idea.