Here is something you can try. Engage the PTO with the lever by your foot. You should always do this at idle or as slow as the engine will let you engage without the implement stalling the engine. In this case you don't have anything attached so it should engage at idle. If you have a grinding noise then the clutch still needs adjustment.
Then while at idle, observe the PTO shaft as you change back and forth between the speeds. You should be able to easily tell the difference.
If there is no difference, then something inside is not working as it should be and you are probably stuck in just one speed. If it easily changes speeds so that you can notice, there should be a neutral position in the middle. Kill the engine, leave the front lever engaged and try turning the PTO shaft by hand as you move the speed lever. You should be able to feel the selector change and feel the neutral spot in the middle.
I have had the 3 point off to work in the differential but it was before I had the snow blower and had not used the 1000 speed. I suspect it is just a case of the slider not going on the gear as far as it should. In any case it has not been enough of an issue to warrant the work required to look at it. And I usually forget about it until it is too cold to work on it anyway.
You might be able to see what is going on if you had the entire axle assembly out, but I doubt you could get to it to perform repairs. Taking the tank off would be way easier unless you had a reason to pull an axle for something else.
If you have the rectangular cover plate just above the PTO shaft you may be able to take that off and with the help of a mirror or borescope camera see what is going on. That cover is where the backhoe hydraulic pump mounts. I am not sure if all 200 series tractors have that cover plate.