hydrailic feed for chipper trouble

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I'm operating a tractor (kubota something or other I'm guessing ~40 HP) with a brand new valby 900 chipper on the back. I can't get the hydraulic feed to work properly. it works as it should at idle to about 1000 rpm PTO speed but when I bring it up to operating speed (PTO at 540 rpm) the hyrdrualic feed will not stay operational it cuts out and the lever in the cab pops to a neutral position. I am bringing the hydraulic feed into operation in the cab with the lever at idle and then ramping up as I was told to do but I can't get the thing to function at speed.....

HELP!!!!

PS the tractor I'm trying to operate is NOT my b2400!!!

 

[stayalert]

details to follow....Shop that set it up is sending mech. Current thought is trouble is associated with couplings.