Zforce 500 side by side and not cforce 500 atv? If the zforce 500 then, make sure the uni filter UP6229AST is on your air filter box. If factory filter is still installed you are likely to have to do and top end rebuild from dust because the factory filters are trash. Also sound like your cvt belt is slipping if your rpms are revving up in high gear. The cvt could also be packed with dust and the belt burnt up from bad driving habits of running the machine in high gear at speeds less than 20 mph and up steep grades as well. Keep an eye on electrical issues like thr thermo fan switch, oil pressure sensors leaking oil, speed sensor failures, ignition switch contact corrosion. Check suspension bushings for proper greasing, change the coolant if it hasn't been changed out yet.