Fordomatic late shifting ('57 thunderbird)

[yblock57]

Update 12/17/20 — issue in this case turned out to be the throttle valve installed wrong in the valve body. Dominic Hide nailed it in post #23. His picture shows one that was stuck. Mine ended up being installed incorrectly by the rebuilder. Once this was corrected, the transmission shifted correctly.

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Howdy everyone. Apologies in advance for the long post. Any help you have to offer is greatly appreciated! Done a lot of reading on here and elsewhere and can't seem to find a solution.

Looking for some advice/direction on how to solve late shifting and very harsh downshifting issues on a medium-case Fordomatic in my '57 bird.

Background:

Transmission was rebuilt by a local trans shop that specialized in older stuff. We pulled engine out to keep costs down and took trans in for a bench job. Everything went back together fine. Shift points are very late (30+mph regardless of throttle pressure) from 2nd to 3rd. It also downshifts back to 2nd at around the same speed (harsh).

All linkage adjustments were checked and reset several times per the shop manual to try and remedy. No change in shift points — it doesn't matter how far the rod is shortened or lengthened. Car went back twice to the shop and they basically threw in the towel and said that's how it works. Car went to two other shops where the valve body was dropped and they discovered a sticky throttle valve. This also made no difference to the shift points. Reset linkage again and no matter where the adjustment, car shifts same (late). In fact, it shifts the same with the kick-down rod completely disconnected. Something else is going on here.

The transmission goes into gear very quick and crisp from park to reverse, drive & low and shifts nice and firm — just late. From reading the Fordomatic manual, I was leaning toward the governor being a possible issue. I pulled it out and it appears to be in good shape. Piston is not sticking and no contamination visible. Appears to have been installed correctly. (Was hoping it wasn't and would be the cure to the problem.)

video of governor:
https://youtu.be/yBX84igvJ2M

We have a couple of other cars with this same transmission and have no problems adjusting the shift points with the kick-down rod. In fact, they're fairly sensitive to small adjustments. They all can be made to shift around 22 mph per the shop manual as well.

Should I be looking at something else? Fluid is still very nice and red and fresh smelling. Running Type F. Only a 150-ish miles put on since the overhaul. I really hate to have to pull this thing back out again. Hoping it's fixable in the car!

Thanks in advance!
Kent