We have a Kom PC 220 LC-8 which has a travel problem of the drive stopping or the brake applying for a millisecond in all travel speeds. It does this going up or down hill, even with the track lifted off the ground. Which causes rough jerky traveling, we operate in low or medium most often.
Had a problem sounds the same on u55-3 smaller machine I know turned out pilot pressure settings to high when tracking joy sticks would vibrate causing boom functions to operate dropping Hyd flow to track motors try holding sticks steady tracking in high just a thought