Rear shock tower. Buy the cf towers. Get some front control arms. Get a set of diff spider gears and a diff carrier. Get at least one set of hub bearings
These are the primary pieces that usually mess up at the worst time and can't get very fast in some cases. If you are on inconsistent tracks(bite,no bite and rough) I would strongly recommend these parts. Diff parts don't break frequent but they do break and usually it hurts the diff carrier