My husband and I noticed that my Hyundai Elantra (2007) sounded rough when running over 60mph. The car has 61,000 miles on it and is due for an oil change, a radiator flush, and a fuel filter replacement. My manual says that the platinum coated (versus iridium coated) spark plugs would need to be replaced at 60K miles. I was told that the car would run rough at lower speeds if it was the spark plugs.
Based on the information I provided, does anyone have any ideas about what the rough ride at higher speeds would be pointing to?