Does the gauge stick on full or empty?
If always full, you have a short. If always empty, you have a break in the wiring.
You mention you've changed the lift pump, but did this include the level float and it's carbon track too? Does the needle move at all as you plug/unplug the level sensor at the tank?
Have you tried leaving the lift pump/level sensor in the tank (to reduce the risk of fire), unplugging the pump/level sensor and connecting the cable to one of your spares, then manually moving the level float to see if anything changes?
Have you tested your replacement level sensors with a multimeter to be sure the resistance changes as you move the float?