02 X type runs at 2700 to 3000 rpm on highway is that normal? I do have 18 inch chrome rims if that makes a difference. Also, had gearbox fault once, wouldn't start so I replaced battery and like new. A few months later, driving from Georgia to Michigan had a gearbox fault while driving. Stopped into autozone and bought fuel cleaner, gas cap and hooked up code reader. Piston misfired and some codes I can't recall but car still running to this day with no fault since. What could be the problem?

 

Should be about 2500rpm at 70mph.