I had a very similar problem with my Intrepid. Three of my spark plug wires were cut. Not completely through, just the insulation. On turns or bumps, the wires would come near the valve cover and cause a spark. Since the spark no longer occurred at the spark plug, it caused a tremendous loss of power. Sometimes it would idle on three or four cylinders. Check your cables, spark plugs, try different brand of fuel... check your timing.