Changed the pump diaphragm, turned out the old one was probably fine but was installed wrong side in and the cover was barely locked in place.
Road test, no difference.
Then installed a new vacuum splitter valve (the white valve on the VC).
Road test, no difference.
At this point the predicted fine day turned into a nasty afternoon of thundersorms so that was it for the weekend.
The buddy who was helping me (he having small hands, me not) wants to try switching over the modulator valve from my parts tranny, next weekend. I figure at this point it's a waste of effort.
By the way, I probably not been describing the symptoms as well as I might. It isn't stuck in first... rather when it tries to go into second it loses drive. If you let it scrub off some speed it picks up first again, albeit in a slippy way unless you stop and start off again.
I am thinking of writing up a new thread on this, just in case someone hasn't picked up on my previous ones.
Thoughts?
