Crazy Gas Gauge

[Sears]

I have this weird problem when I fill up my DII. If my gas light is on (the problem does not occur if I fill up prior to the tank being almost empty) and I fill all the way up, I start my truck up and the gauge goes to full. After driving 30 seconds, the gauge dies (drops all the way to empty), the light comes on and then after a moment it rises again to full and continues to operate normally for the rest of the tank. It happens like clockwork if I let the tank get all the way down to where the light comes on. Anyone know what may cause this? Is the sending unit going bad? I know, I know the easy way to fix it is to fill up before the light comes on. This problem is so odd it just makes me curious.
Thanks

 

[rmuller]

I had the same thing happen to me on a 1990 Volvo 740GL .. good thing was, I was a college student at the time, and very rarely had enough money to fill the tank up.. so it didnt bother me very much [never bothered to try to solve it]