New transmission, maybe like 500 miles on it.
Truck acts like it is in "neutral" when you slow way down or stop. (not moving the gear shift)
It doesn't wanna go unless you rev up the RPM's a ways and then it kicks in. Almost like I'm running a manual with a clutch.
Any thoughts?

Fluid level?

Checked it when hot and running and it was at full, and may be slightly above Full

Is it possible that I have the wrong dipstick and it is reading full but still a couple quarts low? To my knowledge I put 2 in the torque converter and only 6 more in the trans before it read full and maybe I’ve put 1/2 quart more in it since.
Using a deep pan.
So only 8.5 quarts in it??

Might be wrong dipstick or tube. Should be a part number on the stick. With the deep pan I would expect full would be close to 10 qts.

What kind of converter is it? Stock?

YesSir, F48. Went with the stock TC

Ok, finally got some time to start the bronco and let it get up to temperature.
I put another 2 1/2 quarts in it without overflowing it out of the dipstick tube.

It went right into reverse and moved under its own power, stopped and shifted into drive and there was a slight hesitation and had to slightly increase RPM’s to get it to move forward but then it ran pretty good around the neighborhood.
When coming to a stop it acts like it wants to die and does not shift down into first gear, it stays in second but I can manually put it in first or I can Goose it and it will downshift into first and it shifts back into 2nd, but the same thing for third, it didn’t want to shift into third at all.

When I got home I didn’t look exactly where it was leaking from but possibly the vacuum modulator?

You should bring it over sometime so I can take a look at it.