It’s my experience and understanding that even with zero vacuum gong to trans, it should still shift through the gears. You’d have some rougher downshifts, and the final one into 1 will clunk. Not shifting out of first is not likely a vac issue.

I figured out a leaky vac lock system on mine. First off, i’d close off the hvac green line near the south in engine compartment, and leave that stuff for later. Diagnosing those leaks is way more of a pita than locks - and you’ll likely need the dash out.

The locks you just have to methodically go though each door and the tank in trunk - testing with mityvac. Take out the removable floor carpets, learn how to disassemble the door cards so you can get inside the doors to inspect each vac element. This is pain but after doing it like 8 times I became an expert. The vac diagrams are helpful but I will say that our friend Kent at the “source” does have a very helpful booklet on the lock system that I found key in my diagnosis.