Cat E120 B excavator

When I swing the boom it goes very slow unless I introduce another function like boom up or bucket crowd or dump then it goes at normal speed as well left hand track is very weak unless I'm using the right track at the same time . I have just had the motor reconditioned and put a new PR valve in as well as new injectors and the injector pump has been looked . I have put new hydrolic filters and oil in and the hydrolic pump was reconditioned 170 hours ago .i have had it at a work shop and they switched the main hydrolic hoses around which changed the problem from stalling the motor with boom up if you didn't introduce a nother function has anyone got any suggestions
Regards wayne

Cat E120 B excavator