I had the AUX tank sender go-bad on my 2000 Chevy K3500. It rotted-out and failed causing the MAIN tank to run dry. I replaced the sender but I'm not really sure it is working properly since both tanks are FULL. One peculiarity exists, however. When I turn-on the key the gauge reads HALF and stays there for about 30 seconds after I start the motor. It then snaps to "E" and stays there.

Why is it reading HALF when the tanks are both FULL and why does it snap to "E" after 30 seconds? Can anyone venture a guess?