a couple things you should be able to do, since it is a kawasaki twin motor.
filter kit and FMF slip-on exhaust for starters. this is 4x4 and a belt drive clutch, so Maybe EPI (Erlandson Performance) can set you up with some clutch tuning.
We could help you more in that respect if we knew exactly what is in the clutch
This thing is EFI, so you prob will have to ask a dealer if a new ECU is available for it
I think he might have broke something,because he was going about 1 mph and like a snail but the thing is he was a die hard, props to john deere,with a flat tire..