2001 deere 50c zts. problem real head scratcherany input would be great

Hydo problem



The machine has great hydro power dig boom arm swing but when you track its slow to no movement.



But when you hit the relief like extending the thumb circut to max and hold it there the propel motors (tracks) r move as they should. Power



Deere enginers are stumped aswell

Pump pressurs good flow good



Could the combiner valve?

Crossover?



Why would pressure back feed the valve.



Im stumped

My number is 2537224123 if you need to call



Thanks

2001 deere 50c zts. problem real head scratcherany input would be great