B6 AT Shifting problems

[MazdaNut]

I've got a '95 RS (B6) automatic with 167k miles on it.
I picked it up cheap, and put a new(er) engine in it.

I'm having problems with the transmission. Here's
what it's doing. It shifts OK from 1st to 2nd, but then
when it comes time to shift to 3rd, it will downshift to
1st instead. Lift the throttle, and it shifts back to 2nd,
but never higher. It's not slipping or doing anything
unpredictable otherwise. It's very consistent.

I tried adjusting the throttle linkage cable (I seem to
have misplaced my line pressure gauge, so I used
the old driving and stopping method). It changed the
shift quality from 1st to 2nd, and even stopped it from
downshifting at one point, but still no 3rd or 4th.

Solenoid resistances are all 16-18 ohms. I couldn't
get to the vehicle speed pulse thing to check it. Has
anyone ever heard of that going bad? The fluid is dark,
but not black. I replaced some with a popular additive,
with no effect. Timing is good. Idle is good.

Is there a way to manually shift it into all the gears?
I don't see anything in the factory manual.

Thanks for any ideas.