Erratic fuel gauge?

It would jump from reading full, to reading empty, to reading correct. Most of the time it read empty. The truck ran fine in spite of the fuel gauge. The sending unit is part of the fuel pump so a purchased a new fuel pump, lifted off the bed to access the top of the gas tank and traded out the pump and sending unit. My old pump had two electrical connections and while the new pump had two connections as well one was a different connector which required cutting and splicing into the existing wiring. Not a big deal. I spliced in the new connector and installed the new pump. Time to test the installation. Two things occurred. First was that turning the key would turn off all power to the truck, I would disconnect then reconnect the battery and everything would reset, but again every time I turned the key it was like the truck would go completely dead. By mistake, after jumping in the truck I pumped the accelerator a few times, then turned the key and this time when I turned the key the truck cranked. It didn’t want to run at first, but I attributed that to the pump needing to refill the lines to the engine and getting air out of the lines. Eventually it ran and then started up consistently time after time. Now that the truck was back to running, I have my second issue. The fuel gauge is still not working; however, it is a different issue than where my issue started. Before the gauge was erratic, now it is just on empty. (Well, way below empty). (Confirmed The tank is not empty; it is maybe 3/4 full). The gauge reads almost 180 degrees around from where it should be. The pointer on the gauge is pointing down, (should be pointing up) below the increments marked on the gauge. Do I have a faulty sending unit? Do I have a wiring issue? I checked my spliced connections, and they look tight and per the included instructions. I checked fuses and all seem good. I pulled the pump and sending unit out of the tank again. What can I trouble shoot next? Thanks.