1983 Cat D4E with powershift not moving

Hey guys,

I have a 1983 Cat D4E with powershift trans not moving.
I was pushing a small amount of dirt and it just stopped, not loud noises or anything.
You can feel the gears shift but no movement or binding on the motor.
Just looking to know where to start, anyone have any common problems or suggestions?

Thanks

1983 Cat D4E with powershift not moving