23s seem to have odd issues. If you bought the car used it may have been tuned and put back to stock but they didnt return the trans to stock and its looking for a higher RPM to shift at that never comes. My used 18 was like that. Jon Moored tuned my engine and trans, just a tune nothing else and it fixed the issue, and the car ran amazing. Makes my stock 23 feel like a Camry at times.