Left travel very slow/weak

I am having a travel problem with a Hitachi Ex200. Left travel is weak/slow. If I actuate the control levers while I am trying to track the machine, the pressure to the travel seems to increase and travel speed and strength in the left side increase. Main relief pressure is normal on both pumps. Could there still be a leak in the Center Joint if main relief pressure is good? I am still learning as I go, so please forgive any dumb questions I am not sure where to test the pump control relief. Can anyone tell me where the best place to check that is and what the pressure should drop to with pilot activation? Any other Ideas or suggestions would be helpful as well.