98 dakota 5.2 magnum cutting out

working on a 98 dakota 5.2 magnum.runs great,then it acts like its running on 7 cyls.or 6. i just tuned it up.new cap,rotor,wires plugs.and oil change.it was already having this problem before i did anytthing to it.i was thinking clogged fuel filter ? bad pump?anyone?