13 speed still grinding

When I took the back box off I was expecting to see brake material gone from the synchro, however it still had some life in it. I had synchronizer replaced anyway and a gear replaced along with o-rings on splitter and range cylinders.

 

I also replaced air lines on tranny, regulator, and replaced o-rings in slave valve. Could a plugged vent do this? I have not replaced air line to the transmission yet, its crusty.

 

I haven't checked air pressure yet. I will round up some stuff to test air with. Is there a way to test slave valve?
Yes,260 is the cats meow

 

Does the main supply line come in from the floor near the brake valve?
1990 Pete 379

 

Made a line and gauge to check air pressure at regulator and got about 115 psi, so I was going to check the outgoing pressure but needed a different fitting. While I had supply line off, I replaced it and added a bunch of marvel mystery air tool in the line. Drove truck down to get fitting's and had no problems. On the way back still good so I went for a scenic drive and it's working fine so far. So, I think the slave valve may have been sticky, even though I rebuilt it and am sure I would have lubed it too. Anyways, thanks for the ideas and hopefully problem solved.