Throttle cable and kickdown cable pulling hard

You checked for wot, im sure and it has full return? This setup has different geometry than original i imagine.
Comparing it to original setup or your daily driver?
The trans kickdown has resistance
When you pull it by hand?
Usually there is very little drag.

Feel different with trans cable off?

Yep. Full throttle.

Full return as far as the cable will let it go. The way I read it, you adjust the kickdown at idle, by opening the kickdown arm on the trans until you just start to feel it resist from internal pressure.

But yes. It fully returns to that point.

This car had nothing when we started. We had no kickdown linkage, rods, or bellcranks. The cable seemed like a simpler way to go.

And it's stiff in comparison to any car old or new I've ever built or driven. It's pretty stiff.

You can feel as you push the lever on the trans it gets harder to push as you push it back. And when you let off it springs back forward.