Kubota RTV 500 trouble climbing hills or pulling 500 lb load

[Diver94]

Older Kubota RTV 500 used lightly around our small farm, feeding a few hay bales or checking cattle. It has begun to hove low power, to the point of not climbing a hill in high, or pulling wood splitter. Tuned it up and changed filters with no change. Good machine, but it is almost useless as is.

 

[plastikosmd]

Is the engine changing in rpm as it struggles?