The JT chassis kit includes the main chassis plate, front and rear shock towers and front and rear braces. Its well worth getting as it strengthens the truck immensely.
As for the gear change, mine was screwed way too far to the right (late change) when it was new. I had to screw it all the way left then all the way right to find out how many turns would be central. If you are unsure whether your truck is changing or not, it isn't. The engine change is definitely noticable and if you hold your truck in the air whilst revving it, there is a definite kick when second gear engages.