As a general rule of thumb, one should always replace the fuel filter when replacing the fuel pump, i don't think the fuel filter is that expensive so i would agree with your mechanic if you haven't changed it in a long time (typical fuel filter life is about 50,000km). Keep in mind it might also be your main relay, as those things can cause intermittent fueling issues and may look like a fuel pump problem, you can check that by checking voltage at the connector under the rear seat between the yellow/blk wire and the blk wire as you turn the ignition from off the run position. You want to check several times to make sure the relay is putting out a solid battery voltage. If you check it and once in awhile it puts out less than battery voltage (eg. 7V) or is fluctuating, you know you have a bad relay and you can replace or repair it if you know how.