I have a 580b it won't go forward. Trans pressure is in the red when in forward. Goes in reverse fine. Also when lifted off the ground at idle in neutral and forward tires are powered in reverse. If you give it full throttle in forward with the tires off the ground they will spinn forward slowly. I tried changing the filter and fluid it made no change
Since it works in reverse, you can eliminate anything that is used in forward and reverse. Things like the torque convertor, oil pump, that kind of thing. So that leaves the oil circuit, valve, and forward clutch pack as the suspects. Hope you have a manual, you'll be needing it to diagnose this one. You need oil under pressure, so start with that. Find out where the oil is or isn't.