Build up your drivetrain with metal drive shafts and i even installed a robinson racing steal tranny the plastic has to much flex. You could also try a tunned pipe i reccomend the THS pipe.
Okay, you are not going to want to put steel gears in your transmission. Your tranny is strong enough already as it is without spending 80 dollars for useless gears that WILL still strip if something else is broken. It's like this, you can spend 5 dollars if a gear goes out or 20 if a metal one goes. But I would recommend CVD's. Less rotational mass and nice and strong. You can upgrade your tires and change out your gearing. A nice Pipe would be good as well, something like a Resonator or THS.
robinson diff gears wouldn't be a bad idea....
changing out your spur gear/clutch bell will help out a bit.
MOTORSAVER filter! like the k&n for nitro rc