Truck Repair: hesitant accelleration los of power, fuel water seperator, accelleration

Question
Driver came in a week ago ask for a fuel water seperator change. Said the tank had water in it at another place when checked. drove to ythe shop complaining of low power again. changed the filter, and seemed ok for about a week. Has been refueled and don't know condition of fuel. once checked, and if it is ok, if I change the filters again, could it be electrical, or both. I drove it around the block, and when I gave it full throttle, it didn't seem to have any pep. This is with no load, in a box FL70.

Answer
I wouldn't think electrical for the simple fact that changing the filters makes it go away. If anything i would think maybe a fuel pump going out. What engine is it? To take care of the water in the tanks you can get some additive at napa that gets water out of the tanks dont remember what its called but ive used it and it works good. How does it sound at idle and giving it gas. does it sound missing or starving for fuel or air? You getting any color of smoke?