Cadillac Repair: fuel pressure, gas tank, fuel filter

Question
my fuel pump humms while giving giving gas at speed of 20-50 mph, i changed the fuel filter and the gas was black and it ran great with a lot more response for about 15 miles and then ran sluggish again and the humming came back, that was 300 miles ago. im going to change the filter again this weekend just to see how it looks and im going to check my pressure also. any idea on what the pressure is supposed to be at idle and what not? thanks

Answer
You had better remove the gas tank and flush it out as you have accumulated some JUNK in the gas tank that is plugging/restricting the flow of gas thru the pump filter in the tank at the bottom of the fuel pump and in your fuel filter that you replaced before you damage the fuel pump.