NASCAR is a sport with many ups and downs. The winner one week could barely finish inside the top 20 the next. Over the course of a single race a driver could be leading laps one moment only to end the day on the hook of a tow truck. With 36 points-paying races that span from February through November, it's doubtful the drivers highlighted below will struggle each and every week. However, there is a question mark or two surrounding them due to key team changes, troublesome trends or simply some doubts about duplicating last year's success.