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Biggest upgrade part would be the shocks, I believe these were a step forward from the 2014 model onwards.

I would be doing the brake disc and pads for performance gains.

But biggest upgrade is practice and trying setup changes for this you will need money for tyres, fuel, springs, diff and shock oils etc.

And then if money allows look to reduce some weight out of the driveline from changing front and rear shafts, two speed oneway, two speed hub, and brake pulley.

But the biggest performance gain will come from practice and trying setup changes for this you will need money for tyres, fuel, springs, shock & diff oils.