Probably just the gearbox and bulkheads.
The best way to describe a Traxxas kit on a track is floppy. They're built to take the punishment of inexperienced drivers and bashing, and so they're flexible in all the wrong places for racing. It's just not their market, and they sell plenty of...
Exactly.
If you want to be remotely competitive in ST, which you're already handicapped with a a Rustler, 2.2" ST tires appropriate for the track, and drop it a great deal. You'll also have to figure out springs and shock oil for the specific track, but I'd start with medium rate springs...