Can you find on the tractor where it says who made it?
I believe it is a Mitsubishi.
Trans or rearend???
Try the differential lock.......easily.
You can take the Rockshaft arm section off in one piece usually, that will allow you to see down into the rear axle area.
Could also be the coupler between the hst and the mainshaft.
If you were pulling hard etc, this could have stripped.
If this is the case, you should be able to lift the rearend and make it work, for troubleshooting purposes.
TAKE IT OUT OF 4WD......first.......
It won't move the tractor but it will allow everything to move because it won't have pressure on it.
As others have stated, try all the easy stuff first, Hi-Lo lever, 4wd lever.
I have been on a couple of trouble calls that just needed the lever moved, lots of levers can be in nuetral.
Good Luck
BTI