Fuel delivery to the pump has to be 100% , even if you find the filter ok, but i daught it, tank strainer it's the first think i'll check, also you can blow air on the lines to make sure you don't have a obstruction but it's rare this can happend , in my case before I was fixing my own cars I had a problem whit a trailng arm on a 300 SD and the mechanic pushed agains a fuel line and colapsed the line , that car never drove the same from that moment for about nine months , all the "experts" made me spend money on all kind of stuff next on line was a rebild transmition ..thanx to brake job on the rear wheels I was able to see the fuel line crushed .. the rest is history.