Recently got 2002 e150 van with 5.4L v8 which stumbles at times going uphill. It hesitates at other times while accelerating or moving from stop. It even bucks on occasion until I take my foot off pedal and reapply. Happens at various speeds. No such problems while revving engine while in park. Diagnostic gave "cylinder #5 misfiring" mssg. Put in new plug and coil w/boot. Drove GREAT for 2 days then back to same old thing.