First thing are you sure it's fuel pump that was issue if you are still having issues? Assuming it is, the fuel pump runs at 2 different voltages, a lower voltage and a higher voltage at full throttle. Does it still lag if full throttle? Possibly the lower voltage is to much for the new pump. If so you can hard wire bypass the voltage step, plenty advice on SAU if you Google. Also very importantly make sure you are not getting an engine light or anything when testing this, if there is a fuel supply issue you don't want knock or leaning out.