Fuel gauge woes

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?

The IPC fuel level isn't actual, like previous models with the tank switch duals, or single tanks. Late models with the transfer tanks are cumulative, meaning both sender levels are interpreted by the PCM, the the output to the gage should indicate the average level of both tanks, and allows for the dynamic transfer process. Either one/both sender is not sending correctly, or it needs to be calibrated (the PCM sees it as "foreign" data). Possibly why it shows 1/2, then E, once the PCM/BCM is fully booted to run mode. You'll need 2 full tanks, and a Tech II (or compatible) scanner to calibrate. If a battery disconnect (30 minutes or more) doesn't reset it, there's no "automatic" or end-user available method that I'm aware of. If it's "out of calibration", there should be a related BCM code. Usually, the problem is a poor connection (or a forgotten connection).