Cadillac Repair: 90 DeVille runs rough when gas tank is half full, electric fuel pump, full tank

Question
The car runs good with a full tank of gas, but when it gets down to 6 or 7
gallons remaining, it starts to run rough, and eventually turns off.  After a
while it will crank back up and run ok for a little while, then turn off again.  
When I refill the tank, it runs ok again until the tank gets back down to 6 or 7
gallons.  What could it be.

Answer
There is a small rubber hose that connects the electric fuel pump to the metal fuel line pickup tube in the gas tank. This small hose is famous for developing leaks and needs to be replaced as when the fuel level gets below the rubber hose you start sucking air from the gas tank.