Cadillac Repair: 1987 cadillac cimarron, cadillac cimarron, fuel mileage

Question
New plugs, wires, air and fuel filter, pvc, ecm. It is not showing any codes. It runs ok, idles ok. Its only getting about 15mph highway. Its not burning oil. 180 k on the motor. Any suggestions on what might be causing the poor fuel mileage

Answer
Is the over drive working correctly ?.

Are you having any intermittent stalling when coming to a STOP or when you shift the car from PARK to DRIVE ?.

Some people have said that by replacing the oxygen sensor that they have improved their mileage by 2 or 3 miles per gallon, But I do not know this to be factual.