BUCKING JERKING

What is your question?

AT 65MPH WHEN I APPLY GAS THE ENGINE BEGINS TO BUCK OR JERK VIOLENTLY. I HAVE REPLACED THE THROTTLE PRESSURE SENSOR. REPLACED FUEL FILTER. REPLACED SPARK PLUGS. WHAT ELSE SHOULD I DO. THE VEHICLE, GET 28.5 MILES A GALLON ON THE OPEN HIGHWAY. GOOD GAS MILEAGE. BUT THE BUCKING HAS PUZZLED ME. THE ENGINE LIGHT IS OFF. LARRY R.