Next step would be good back to post #2.
The work you have done is changing parts, and making and repairing connections, but no indication that you have used a voltmeter to troubleshoot circuit connections. The circuit starts with 12V supply to regulator, then output to gauge, then to sender and return at ground. Any open connection results in no worky.
So check 12V at regulator input, check if the regulator has output, check it making it to gauge and out, and sender returning to ground. The sender ground at tank needs a metal clip that jumpers the rubber hose and connects tank sender tube to fuel line that is grounded via all the straps to body. The temperature sender body grounds at thread, Teflon tape can insulate. Senders also fail open, so do Ohm check.
