Fuel gauge racking my brain..

Okay guys, seeking help from the forum. Got a 2001 GT. Fuel gauge is showing open circuit. I've got a digital dash, Intellitronix but this was happening before I even started, installing the dash. I have yanked the tank numerous times, replaced the fuel level sensor, pump, and hat. With the pump / hat assembly out of the car, and plugged in, ignition on, can move the swing arm float, up and down, gauge reads normally. Just finished reinstalling the tank yet again, turned on the ignition, did not start it, and started filling the tank. Watched the numbers climb as she was taking fuel. Got about 10 gallons in, low fuel light came on, threw the p0460 code, and then the fuel level dropped back to zero. Again, has this happened,as well, when I had just the regular gauge in it. Basically have rebuilt the hat, the wiring in the hat, and the pigtail that comes off the top of it. Fuel sender checks out great with the ohms, good continuity through all the leads with no resistance as well. Has anybody experienced this headache with their tank/sender? This is driving me nuts, every time I think I got it fixed, it repeats the same process. I'm actually leaning towards something going on in the ECU. Any input appreciated guys. Thanks in advance.
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I would install a temporary set of wires from the sender to the cluster. This will tell you if it's an intermittent wiring issue or a bad cluster/gauge. IF it's neither then you're left with the sender.
The fuel gauge doesn't go through the ECU. It's a direct shot to the dash, so there may be something else in conjunction with your gauge/sender. I would double check the pin(s) at the plugs as well as the grounds. Check dash input plug as well. If you've done all that as you've described, the next best test would be to mock up the sender in a pail of liquid (doesn't need to be gas) and actually watch the sender in operation along with the gauge. You may just have the sweeping resistor giving you fits.