Sometimes it helps to recheck some of the basics. You should read the FAQ on replacing the fuel pump. At the very bottom of the FAQ is a photo of the fuel pump inlet filter screen.
The biggest and most prevelent problem with these fuel pumps is that this screen is either too fine or too small or both and that it plugs up too easily. If you have even a small amount of contamination in the tank, the filter plugs up just enough to cause fuel starvation under load.
So you may need to more thoroughly clean out the tank. You may also need to do nothing more than remove the filter screen and throw it away. It isn't needed. There is still a conventional sock filter on the inlet pipe further inside the fuel pump module.
http://www.contour.org/mods/mods.php?s=howto&displayid=39 
