I have a 99 cherokee sport. Just had new plugs, wires, distributor cap, and rotars replaced. Took on its longest trip ever. After it got down to about half tank of gas it would cut out if you got on it, until you let off and ease into it. After stopping and refueling it didn't do it again until about half a tank. So I refueled again, and was fine. Haven't got back to half tank since yet. With no problems. FUEL PUMP or what. Please help