hi,this is a very good car.i brought one,the main parts are the hub carriers,upgrade to ally one's as the screws tend to strip out.the diff's are already upgraded on the 18ss so no need to worry about them.i would also definatly consider upgrading the air filter and exhaust. i have just fitted a tsasi nitro devil rear exhaust and it has made a big difference,but hpi don't make good exhausts so any exhaust is probably better.
good luck with the car and enjoy mate