Chevelle Fuel Gauge Problem

[Damien]

Hi guys.
The fuel gauge in my '70 SS has never worked correctly since owning the car. Has never read past half and at one stage didn't work at all. All the gauges were replaced by the previous owner with repro stuff. I have tested the sender in the tank and all seeems ok so it looks like a ground or a gauge issue. I have found 3 grounds under the dash, one on the e brake bracket and two under the dash, mounted together onto bare metal. Should there be one or two more grounds under the dash that I haven't found? If the grounds all check out it, have I confined it to a gauge or electrical dash issue? Is there something obvious I have overlooked? Just trying to eliminate everything before I take on the job of pulling the dash either part way or completely out of the car. Any suggestions appreciated. Thanks in advance.