Bobcat 331 boom hydraulics

I have a bobcat 331 mini excavator serial # 512915703 that when operating the boom hydraulics get slow and then stops working completely within 5 minutes of operation. the machine still has full power until it quits but you can shut machine off and start back up and everything works until it decides to stop again. Since when got machine recently we have changed one track motor that was out when we purchased it and we changed the left joystick control for the up and down of boom and swing we checked pump pressure and even when it quits lifting the pumps maintain the pressure they should have. I’m at a loss on what it could be wrong and any help would be appreciated thank y’all