Kubota U35 hydraulic issue while using brush cutter

Hello, I have a 2013 Kubota U35 Super Series that I am having a issue with but only when using the brush cutter, While the cutter is running all motion on the machine works normal except extending the arm, It retracts normal but moves away very slowly, the the boom, bucket, rotation and drive all work normal with cutter running, The arm does work normal with the cutter off.
I am using the max flow on the excavator and have the return port valve on the tank open as it says to do, Is there a separate priority valve for all boom functions or what could be causing this issue? Thanks

Good day
Are you using the arm pump to give power to the brush cutter? maybe the attachment has priority. If you have a hydraulic schematic it will be possible to check it out.Its guess that with the brush cutter having direct return to tank the flow will go in that direction leaving only the remains for the arm. The arm will fall inwards opening the check valve but going away from the machine will require power.
Kind regards
Uffex

The Kubota dealer gave me a idea to try on it, There is a function to limit the max flow to the remotes, he wants me to back that off some to see if it improves the arm function, It has been too hot out to try that though, I will post back when I find out if that helps, Thanks for your reply!