Could be corrosion on the grounding-strap (Note: strap usually clips onto the sending-unit outlet tube and the steel fuel line beyond the rubber connection) causing the intermittent.

The float could be compromised (if hollow-brass type, partially full of fuel,) wiring or bad-connection, bad gauge, or sending-unit.

Good luck with it. I need to address a similar issue on my '79 CJ5 Jeep, sending-unit on top of tank means I need to drain / drop the tank out to access it.

Ohm meter can be used to diagnose.