[Double Venom]

One of two problems, you're still not matching the correct sending unit to the Autometer gauge, OR since the sending unit you are holding appears to be adjustable for different tank depths, it's simply not adjusted to match your tank.

Hook up your sending unit to the gauge and run the float all the way down and back up manually. If it then reads correctly, adjust the float depth to match your tank. If it still doesn't read correctly, simply call Autometer and order the correct sending unit.

DV...hope this helps