C4 trans problems Plz help

Hey I'm new at this and I really need some help.
I rebuilt my C4 trans the other day and it came out good but something is wrong.

It won't go into reverse if I have the vacuum modulator hooked up.
Ik this doesn't make sense considering the modulator works with up and down shifts but this is what is going on with it.

Can anyone help me?

 

low fluid

 

Did you air test it?