Sumitomo 120-3 problems

Hi all my Sumitomo 120-3 is giving intermittent problems dealers cant find the fault, we thought it was the pump but that seems to be testing fine. it get slow when it warms up, I have to move the levers 5 or 6 times to get it to rev up on auto idle, it loses power when walking the longer I use it. all the temperatures are well with in the working range it some times makes a grinding type of feeling when slewing but the slew seems good I am wondering if it could be a problem with my pilot...

Sumitomo 120-3 problems

Sumitomo 120-3 problems